This study proposes a fiber-optic four-channel dual-balanced heterodyne phase detection method based on optical heterodyne detection principle to realize high-sensitivity heterodyne phase detection. A fiber-optic four-channel dual-balanced heterodyne detection optical path is experimentally established, and a quarter-wave plate is used as a phase detection sample to verify the detection performance. Further, the influence of the signal modulation frequency on the phase measurement result in heterodyne detection is analyzed. Results reveal that the phase information cannot be effectively detected by too high or too low modulation frequency due to the limitation of the response bandwidth of the photodetector. Fiber splitting ratio in double-balanced heterodyne interference and the effect of the effective receiving aperture of the coupling lens on phase detection are analyzed based on the optimal signal modulation frequency of 500.5-1550.5 kHz and the actual measured phase root-mean-square of 89.1° with a standard deviation of 0.3°. When the fiber splitting ratio is approximately 1∶1, a more accurate detection result with a higher signal-to-noise ratio is obtained. The actual influence of the effective receiving aperture on the sensitivity of the received signal is verified by varying the emission angle of the coupling lens.