受海水吸收和散射的影响，长距离水下通信时信号幅度下降，信噪比(SNR)降低，最终导致水下激光通信系统的误码率（BER）提升，最远通信距离受限。为此，提出将最大比合并（MRC）分集接收技术应用于水下激光通信系统。分析和研究了在水体吸收和散射的综合作用下，MRC空间分集接收技术相对于等增益合并（EGC）空间分集接收技术对水下激光通信系统接收器性能的改善。推导了MRC加权系数分配方式，分析了接收支路数目与系统BER性能的关系，采用蒙特卡罗法对波长为532 nm的绿光在IB型水质下100 m处六路分集接收器中MRC相对于EGC的性能改善进行了仿真，并仿真了在Jerlov IB和II类水质下两种分集合并技术BER随通信距离的变化。由理论分析和仿真结果可知，MRC可以根据各路接收SNR情况更合理地分配加权系数，达到合并后的最佳SNR。在同等BER要求下，MRC可以提高水下激光通信的最远传输距离，在同等传输距离下，MRC可以降低通信系统的BER，为水下长距离激光通信系统的工程化提供了一种解决方案。

Due to the influence of absorption and scattering of seawater, the amplitude of received signal reduces and the signal-to-noise ratio (SNR) reduces during long distance underwater communications, which leads to the bit error rate (BER) of underwater laser communication systems rise, and eventually limits the distance of communication. For this reason, the maximum ratio combining (MRC) diversity reception technology applied in the underwater laser communication system is put forward. The improvement of MRC spatial diversity reception technology compared with the equal gain combining (EGC) spatial diversity reception technology is analyzed under the influence of absorption and scattering of water. Weighting coefficient distribution of MRC is deduced. The relationship between receiver number and system BER performance is analyzed. Monte Carlo method is used to simulate the performance improvement of MRC based on 532 nm laser at transmission distance of 100 m in Jerlov IB water with six receivers. In the IB and II type water, the relationship between BER and transmission distance is given for MRC and EGC. The theoretical analysis and simulation results show that MRC can distribute gain coefficients more reasonably according to SNR in each receiving branch, to achieve the optimal SNR. Under the requirement of same BER, MRC can realize the longest transmission distance of underwater laser communication. Under the requirement of same transmission distance, MRC can reduce BER of communication system. An engineering solution for long distance underwater laser communication system is provided.