how to create a circle perpendicular to a line and the centre of the circle is located at one end of the line?

Thanks!

Copy SOP.

On the line, use the PolyFrame SOP and set Tangent to N or normals. Then use a Copy SOP to copy the circle on the XY plane (facing the Z direction as the Copy SOP uses Z as the aim look-at direction to align to N normals or v velocity).

To copy the circle to one of the end ponts on the line, it's either 0 or $NPT-1 in the Template Point Group parameter.

See attached example file.

It is wise to add an UP vector to the line as well to control the rotation

Now there are a great many ways to orient faces to vectors but the Copy SOP makes it easy.

dear jeff, thank you so much for your kind advice!

you method can be generalized to copy any shape along a curve with its normal follow the tangent of each point along the curve.

Note that you can also use the Sweep SOP. You will get two perpendicular circles, one at each end of the line.

Thanks Patrick!

Ji