The intradyne coherent laser communication system with laser frequency fluctuations model is built, and the carrier recovery performance of BPSK and QPSK signals with different laser frequency fluctuation and Viterbi-Viterbi filter lengths are compared and analyzed. It shows that when system is stable, the optical signal-to-noise ratio(OSNR) penalty of two signals is less than 0.5dB at the slight fluctuation amplitude and fluctuation frequency. As the fluctuation amplitude and frequency increase gradually, the OSNR penalty is increasing as the Viterbi-Viterbi filter length values increase. When Viterbi-Viterbi filter lengths are 7 and 11, the two kinds of signals show high performance. For BPSK signals, the average of OSNR penalties caused by fluctuation amplitude are 0.11dB and 0.16dB respectively, and the average of OSNR penalties are both 0.15dB caused by fluctuation frequency. At the same time, for QPSK signal, the average of OSNR penalties caused by fluctuation amplitude are 1.7dB and 2.9dB respectively, and the average of OSNR penalties are both 0.8dB caused by fluctuation frequency. Therefore, for the same Viterbi-Viterbi filter length and fluctuation, the ability of BPSK signal to suppress laser frequency fluctuations is better than that of QPSK signal.