A kind of flatness tester with noncontact light probe is introduced. It has the accuracy of nanometer, with a resolution of 1 nm, and measuring range of 10 μm. This kind of tester shows a great practical prospect in the applications of electronic glass, semiconductor, integrated circuit, thin films and technology of nanometer. Some of the testing results in the study of liquid crystal device (LCD) substrate surface shapes by the tester are presented and the results indicate that this kind of tester can be used in LCD study and play an important role in it.