With sub-micrometric form accuracy and nanometer scale surface roughness, the diamond turning process provides a great solution of fast prototyping optical systems with aspheric or freeform surfaces. On the other hand, with relatively lower cost and lighter weight, optical plastics are now widely used in consumer products. To study and optimize the cutting parameters of the diamond turning process on optical plastics, a series of tests with different cutting parameters settings are conducted on seven different optical plastic materials: E48R, OKP1, OKP4, OKP4HT, PC, PMMA, and Rexolite 1422. The relationship between the surface roughness and optical plastic materials is found, and the optimized cutting parameters are recommended.