Based on chaotic parameter modulation,an M-ary digital communication scheme(CPSM)is designed and realized. The performance of the binary and quaternary digital spreading spectrum communication systems by using different chaotic carriers and spread factors is studied,and those factors affecting systematic performance are also analyzed. The results by computer simulation indicate that the performance of the systems can be improved by enlarging spread factor. In addition,these proposed systems are of good noise immunity,easily to implement.