Abstract: Particle Swarm Optimization (PSO) is a new evolutionary algorithm. In this paper, to improve the ability of the PSO algorithm for detecting global values, the Stretching Particle Swarm Optimization(SPSO), proposed by Parsopoulos, is introduced as a key technique to Code-Division Multiple-Access (CDMA) mobile system. We call this approach the SPSO Multi-User Detection (SPSO_MUD), the experimental results indicate that the performance of the SPSO_MUD is more efficient in BER capability, near-far resistance, and enlarging the system capacity than other detectors.