Coherent polarization beam combination (CPBC) is an effective method to obtain the high-brightness laser with linear polarization. This paper proposed an optical phase modulation method to transform the phase difference between two laser beams into amplitude modulation. Using optical heterodyne phase detection and linear phase-locked control, the polarization beam combination of two laser beams with the same frequency was realized. Further, the mathematical models of optical heterodyne polarization phase detection and linear phase-locked control loop were theoretically analyzed in detail for optimizing the system parameters. After phase locking, the polarization extinction ratio of the combined beam achieves 17.67 dB with the combined power of 352.4 mW, while the control bandwidth is nearly 66.1 kHz. The residual phase noise is 1×10 ^-4 rad·Hz ^-1/2(1 Hz) and 3×10 ^-6 rad·Hz ^-1/2(>100 Hz). Compared with other CPBC phase-locking methods, the proposed method can significantly improve polarization extinction ratio and control bandwidth, and effectively suppress phase noise.