We demonstrate a 202 W all polarization-maintaining (PM) single-frequency fiber amplifier operating at C band. Simulations show that the length of the output fiber pigtail following the gain fiber critically has great impact on the stimulated Brillouin scattering (SBS), posing a major obstacle for high-power single-frequency amplification. Optimizing the length to suppress the backward SBS by ~ 10 dB, we experimentally achieved a maximum output power of 202 W, yielding an optical-to-optical efficiency of 42%. The signal-to-noise ratio (SNR) of signal light, relative to ASE in Er3+ and Yb3+ bands, was measured to be 23 dB and 32 dB, respectively, and they can be further improved by ASE suppression and filtering techniques during amplification. To the best of our knowledge, this is the all-PM single-frequency fiber amplifier with the highest power reported in the C band.