Hi, guys,
I got a very bad rendered image,
but my model is smooth.
anyone can tell me the reason, and how to avoid this?
the model and rendered image in the attachment.
It look to me as if you have duplicated faces. Use ‘Remove doubles’ and then recalculate the normals.
Best wishes,
Matthew
looks like image texture or modifier 
nice result.
Model is simple. It’s easier to send file to get answer
thanks alot,
it is really because the model has more duplicate vertexes.
when i used w->remove double,
the render image became normal.
For future reference, another thing that could be the cause of artifacts is normals faced in the wrong direction.
To fix this, simply recalculate normals outside: [CTRL] + [N]