In this paper, a testing system for groove geometry of CD R substrates by measuring diffraction orders is introduced. This testing is of particular importance in CD R disc manufacture process because the results fed back from the testing can be used to help optimize recording, developing, metalizing, electroplating and replicating processes. Even if the width and depth of groove are not accurately obtained by this system, it is also valuable in CD R disc manufacturing process because the system, which can be used to judge the quality of substrates, is simple, sensitive, quick and non destructive. The results of a same sample tested by our system and an AFM microscope are presented simultaneously.