We propose and experimentally demonstrate the highest-resolution BOTDA system ever reported using Brillouin dynamic grating in a polarization-maintaining fiber (PMF). Acoustic waves containing the information of local Brillouin frequency are generated by a long pump pulse in one polarization, and read out by a short probe pulse in the orthogonal polarization at a clearly distinct optical frequency from the pump. In the experiment, a distributed strain measurement with 1 cm spatial resolution is performed over a 20 m fiber.