The temperature and strain sensing mechanisms based on Brillouin dynamic grating in polarization-maintaining fiber are explored. Based on the transmission characteristics of two orthogonal polarization axes of polarization-maintaining fibers, the relationships between the wavelength, the wavelength difference, the beat length of Brillouin dynamic grating, and temperature and strain in fiber are investigated. The results reveal that the logarithm of the wavelength is nearly linear with the fiber temperature, and the relative change in the wavelength are linear with the strain in the fiber. The difference in wavelength between two-axes and the reciprocal of the beat length is approximately linear with the temperature and strain. This paper points out potential research directions for the polarization-maintaining fiber distributed temperature and strain sensing based on Brillouin dynamic grating.