To address the phase jitter in optical-carried radio frequency signals caused by environmental factors during fiber transmission, which degrades the signal-to-noise ratio after multi-channel coherent superposition, this paper proposes a multi-channel signal enhancement technique based on microwave photonic phase-stabilized transmission. A phase-stabilized transmission system incorporating phase measurement, control, and adjustment modules is designed, achieving stable radio frequency signal phases through closed-loop measurement and precision regulation (10 ps coarse adjustment and 0.1 ps fine adjustment). A multi-channel transmission system is further constructed to realize coherent superposition of three signals using matched filtering and precise phase synthesis. The experimental results demonstrate power enhancements of 4.5 dB and 5.1 dBm at 1.7 GHz and 2.3 GHz respectively, with signal-to-noise ratio improvements of 2.8 dB and 3.44 dB compared to single-channel transmission.