In order to decrease the influence on mechanical performance of smart composite, small diameter optical fibers are usually preferred as strain sensors. Therefore, fiber Bragg gratings in small diameter were manufactured. In applications, the FBG measures both strain (or force, pressure, displacement) and thermal expansion. In order to overcome this inconvenience and to measure both parameters at the same time and location, a simple temperature insensitive force sensor was proposed. A pair of small-diameter FBG was attached on a uniform strength beam. One of the FBG was affixed on the upper surface of the cantilever, and the other one on the bottom. The central wavelength shifts of the two FBGs are proportional to load value F and –F respectively. Therefore, coefficient matrix is well conditioned. The force and temperature in sensing point could be discriminated. Experiments were carried out to study the force and temperature cross sensitivity. Experimental results match the theoretical ones well. The temperature and force were calculated and the errors were 2% and 7% respectively.