According to the coupled-mode theory, different properties of reflected polarization dependent loss (RPDL) of fiber Bragg grating to temperature and lateral force are analyzed. Based on the relevant sensitivity coefficient matrix, the temperature and lateral force can be demodulated by a single fiber Bragg grating simultaneously, by which the problems induced by the cross sensitivity of temperature and lateral force can be avoided in the test progress. The experimental temperature sensitivity coefficients of left peak and right peak of RPDL are 0.0101 nm/℃ and 0.0100 nm/℃, respectively. Lateral force sensitivity coefficients achieve 0.0071 nm/N and 0.0005 nm/N, respectively. The accuracy of temperature and lateral force can reach ±1 ℃ and ±0.6 N, respectively. The key sensing component of the method has advantages of simplicity, high sensitivity and easy to be buried into interior of material tested to conduct monitoring. It provides a new method to test the changes of temperature and internal structure information.