We propose an approach based on the four-wave mixing (FWM) effect for improving the sensitivity of a dual-wavelength fiber laser sensor with polarization-maintaining fiber Bragg grating (PM-FBG). The wavelength interval of the dual wavelength output is proportional to external measures such as temperature and strain. Experimental results show that the wavelength interval can be incresaed using the FWM effect. In particular, we observe that the temperature sensitivity of the conventional laser sensor with PM-FBG is improved from -0.62 pm/℃ to -4.32 pm/℃ while using third-order FWM-based scheme, and a sensitivity enhancement of nearly 7 times is achieved.