We report a high-performance $25\mathrm{km}$ Brillouin-loss-based distributed fiber sensor through optimizing system parameters. First, the Brillouin spectrum distortion and measurement error induced by the excess amplification on probe pulse are investigated, and the results indicate that a low continuous-wave pump power is essential to decrease the measurement error. Then an optimal pulse pair is determined through the differential Brillouin gain evolution along the entire sensing fiber in a differential pulse-width pair Brillouin optical time domain analysis. Using dispersion-shifted fiber to allow a high-power probe pulse, we realize a $25\mathrm{km}$ sensing range with a spatial resolution of $30\mathrm{cm}$ and a strain accuracy of $\pm 20\mathrm{\mu \epsilon }$ , which we believe is the best performance in such a length, to the best of our knowledge.