Yes!You are right Paul, it is because of the ray epsilon!Thank you!

In DAZStudio:
create a primitive object: plane （100m×100m）
give the plane an OC material: diffuse(just use a texture RGBimage)
set the OC environment: sun light
kernel=direct lighting
Then, render the scene: some black circle lines appear on the surface of the image, how can I make those black ...