In order to investigate the effect of signal light splitting ratio on the performance of coherent homodyne receiver, the effect of signal light splitting ratio of 90° spatial optical hybrid on the phase-locked performance of the receiver and the communication performance is modeled and analyzed. From our numerical simulation results, we know that the communication performance and detection sensitivity are improved with the signal light splitting ratio of Q branch k<0.5, and the loop locked-in time is the shortest and frequency-locked range is maximum when k=0.5. In the case of k>0.5, we can obtain an optimal value of k to minimize the residual phase error. Based on the above analysis, we design an adaptive adjustment system with signal light splitting ratio based on a half-wave plate using softare simulations, and its communication and phase-locked performances are analyzed at different splitting ratios. Those results show that under conditions of 1550 nm laser wavelength, 5 kHz linewidth and 10 Gbit/s communication rate, the phase-locked performance and detection sensitivity can be adjusted when k varies in the range of 0.1-0.6 by rotating half-wave plate. The detection sensitivity is improved by 2.56 dB with k=0.1, and for k=0.5, the frequency deviation lock range of the phase-locked branch is 133 MHz. What's more, the residual phase error is the smallest when k=0.6. Those results illustrate the system is feasible and also provide a reference for the application adjustment of the 90° hybrid with adaptive splitting ratio.