Abstract: In ultra-high coherent optical telecommunications, constant modulus algorithm (CMA) is usually adopted for compensation of impairment of polarization demultiplexing and polarization mode dispersion (PMD). Standard CMA has a function of self-adapt dynamic equalizer, with coefficient signal constantly updating according to input signal. It is a popular blind-equalizing algorithm at present. In CMA algorithm, the value of step-size usually severely influences the performance evaluation of algorithm convergence, error vector magnitude (EVM), and bit error ratio (BER). This paper presents an optimized CMA algorithm of two-step size coefficients, which is capable of labeling stable span of error vector function curve. The verification of calculation shows, the optimized CMA algorithm can improve the demodulation performance, decrease the EVM of X and Y polarization state, validating its preferable applicability.