To adapt to the networking technology of space laser communication, the multi-system multiplexed communication mode was developed. In the transmitter, an intensity modulator is used to realize on-off keying (OOK) and binary phase shift keying (BPSK) modulation compatibility; while in the receiver, demodulation of these two modulation signals is realized via intradyne detection. In practical engineering applications, shot noise and thermal noise of electronic devices in laser communication system will inevitably affect the communication performance. Accordingly, the influences of bias point error of intensity modulator and optical filter bandwidth on the signal-to-noise ratio of incoherent OOK and coherent BPSK communication are further analyzed herein. Simulation results show that the optical filter bandwidth significantly influences the incoherent OOK communication performance: the incoherent OOK SNR overhead of 1 nm filter bandwidth is approximately 1.26 when the received optical power is -46 dBm; the coherent BPSK SNR overhead of 20 nm filter bandwidth is less than 0.02 when the received optical power is below -50 dBm. If the codeless communication sensitivity of incoherent OOK is required to meet -46 dBm@10^-6 at the rate of 1.25 Gbit/s, the optical filter bandwidth should not be greater than 0.8 nm, the bias error of the intensity modulator should be controlled within 1% of the half-wave voltage. Under the condition of common-mode noise elimination and optimized optical filter bandwidth, the codeless sensitivity of BPSK communication at 1.25 Gbit/s rate is satisfactory to -55 dBm@10^-6.