In coherent optical fiber communication system, constant modulus algorithm(CMA) is one of the most common algorithm to suppress polarization mode dispersion(PMD). In order to further reduce the bit error rate(BER) after digital signal processing(DSP) of the receiver, a CMA improvement measure based on improving the transmission rate of optical fiber communication system is proposed. The BER of the traditional CMA and the improved CMA are calculated and compared, and the relevant simulation experiments are designed. The simulation results show that the improved CMA improve the compensated transmission rateby 3.46%(BER=0). If the BER requirement is 2×10-4, the transmission ratecan be further improve by 1.33%.