Displacement measurement is one of the most important parameters to be monitored. A Fiber Bragg Grating (FBG) displacement sensor based on double cantilever beams is developed, in which the displacement is changed to wavelength shifts of two FBGs. The influence resulted from temperature to displacement measurement is reduced by the differential of the two wavelengths, since they have the same wavelength shifts when they are in the same environment. The operation principle based on FBG theory is deduced, and the reasons of measurement error are analyzed. Experimental results show that the displacement sensitivity is 123 pm/mm in the range of 0~20 mm, and the temperature crosssensitivity is 17 μm/℃ after temperature compensation. With the particular advantage, this FBG displacement sensor may find tremendous applications in engineering.