A pulse width modulation (PWM) Brillouin amplification has been proposed and demonstrated to improve the signal-to-noise ratio (SNR) and sensitivity of phase-sensitive optical time domain reflectometry (Ф-OTDR) especially for the far end of a sensing fiber. In the logarithmic unit, arbitrary gain distribution can be realized with the customizable PWM function. The gain distribution is adjustable by tuning the PWM parameters. To prove the concept, three typical gain distributions including up-ramp sawtooth, sine and triangle have been achieved with the corresponding driving functions. In experiments, a linear PWM pump light has been used to amplify the backscattering Rayleigh light. The signal at the leading end has been enhanced by about 11.5 dB. Meanwhile, 9 dB transmission attenuation (along 25 km SMF) has also been compensated excellently. To verify the effectiveness of attenuation compensation, two vibrations with a frequency of 100 Hz and 300 Hz have been recovered accurately at the trailing end. Besides, preamplifier and acoustic-optic modulator (AOM) was used to suppress the ASE noise and further improve the effective ER, respectively. With that, lower relative intensity noise (RIN) has been obtained in the proposed system compared to the conventional Brillouin amplification in Ф-OTDR. So the proposed PWM Brillouin amplification not only improves the SNR but also equalizes the sensitivity along whole sensing fiber. It avoids the complex calibration and suppresses the false alarm rate in field application. Foreseeably, this scheme is universal and can be adopted by other distributed fiber optic technique to enhance the system performance.