Hi. 
When two or more link lines between same shapes, the lines overlap.
But, I wish it would not overlap the link lines.

How do I implement?

Hi. thank you.

all examples source code using LinkStyle.Bezier.
but. I want to use LinkStyle.Polyline.
so, I wish to change only start and end position.

In such case try this:

private void diagram_LinkCreated(object sender, LinkEventArgs e)
{
	DiagramLink link = e.Link;
	DiagramLinkCollection links = GetCommonLinks(link.Origin, link.Destination);
	PointF firstPoint = link.ControlPoints[0];
	PointF lastPoint = link.ControlPoints[link.ControlPoints.Count - 1];

	if (firstPoint.Y == link.Origin.Bounds.Top ||
		firstPoint.Y == link.Origin.Bounds.Bottom)
		DistributeHorizontally(links, link.Origin, firstPoint.Y);
	else
		DistributeVertically(links, link.Origin, firstPoint.X);

	if (lastPoint.Y == link.Destination.Bounds.Top ||
		lastPoint.Y == link.Destination.Bounds.Bottom)
		DistributeHorizontally(links, link.Destination, lastPoint.Y);
	else
		DistributeVertically(links, link.Destination, lastPoint.X);
}

private void DistributeHorizontally(DiagramLinkCollection links, DiagramNode node, float y)
{
	float d = node.Bounds.Width / (links.Count + 1);
	float x = node.Bounds.Left + d;
	foreach (DiagramLink link in links)
	{
		int index = link.Origin == node ? 0 : link.ControlPoints.Count - 1;
		link.ControlPoints[index] = new PointF(x, y);
		link.UpdateFromPoints(true, false);
		x += d;
	}
}

private void DistributeVertically(DiagramLinkCollection links, DiagramNode node, float y)
{
	// same as above but replace width/height, left/top, etc
} 

You can't upload files here; instead upload the image on your server or e.g. flickr and paste a link.

I hope that helps,
Stoyan

problem 2: Comparing the link's end point position with node Top/Left/Bottom/Right will work only if the node's Shape is Rectangle. Replace those equality comparisons in LinkCreated with less than and greater than comparison of the link point's X/Y with the node's center point X/Y.

problem 1: The Distribute methods work correctly only for rectangles too. If using other shapes, try calling the node.GetIntersection() method specifying the end points found for a rectangle to get a point lying on the shape boundary.

Try this:

private void diagram_LinkCreated(object sender, LinkEventArgs e)
{
	DiagramLink link = e.Link;
	DiagramLinkCollection links = GetCommonLinks(link.Origin, link.Destination);

	PointF firstPoint = link.ControlPoints[0];
	PointF lastPoint = link.ControlPoints[link.ControlPoints.Count - 1];

	PointF oc = link.Origin.GetCenter();
	float ocdx = Math.Abs(firstPoint.X - oc.X);
	float ocdy = Math.Abs(firstPoint.Y - oc.Y);
	if (ocdx < ocdy)
		DistributeHorizontally(links, link.Origin, firstPoint.Y);
	else
		DistributeVertically(links, link.Origin, firstPoint.X);

	PointF dc = link.Destination.GetCenter();
	float dcdx = Math.Abs(lastPoint.X - dc.X);
	float dcdy = Math.Abs(lastPoint.Y - dc.Y);
	if (dcdx < dcdy)
		DistributeHorizontally(links, link.Destination, lastPoint.Y);
	else
		DistributeVertically(links, link.Destination, lastPoint.X);
}

private void DistributeHorizontally(DiagramLinkCollection links, DiagramNode node, float y)
{
	float d = node.Bounds.Width / (links.Count + 1);
	float x = node.Bounds.Left + d;
	foreach (DiagramLink link in links)
	{
		int index = link.Origin == node ? 0 : link.ControlPoints.Count - 1;
		PointF c = node.GetCenter();
		float h = node.Bounds.Height;
		PointF p1 = new PointF(x, y + (c.Y > y ? - h: +h));
		PointF p2 = new PointF(x, c.Y);
		PointF p = node.GetIntersection(p1, p2);
		link.ControlPoints[index] = p;
		link.UpdateFromPoints(true, false);
		x += d;
	}
}

private void DistributeVertically(DiagramLinkCollection links, DiagramNode node, float x)
{
	float d = node.Bounds.Height / (links.Count + 1);
	float y = node.Bounds.Top + d;
	foreach (DiagramLink link in links)
	{
		int index = link.Origin == node ? 0 : link.ControlPoints.Count - 1;
		PointF c = node.GetCenter();
		float w = node.Bounds.Width;
		PointF p1 = new PointF(x + (c.X > x ? -w : +w), y);
		PointF p2 = new PointF(c.X, y);
		PointF p = node.GetIntersection(p1, p2);
		link.ControlPoints[index] = p;
		link.UpdateFromPoints(true, false);
		y += d;
	}
} 

I hope that helps,
Stoyan