An innovative weighing sensing unit using optical fiber Bragg grating sensors was developed. Based on lever cantilever with an adjustable fulcrum, the weighing range and sensitivity can be adjusted. During the differential operation of the shifts of Bragg wavelength, the shifts of Bragg wavelengths caused by the temperature fluctuation can be compensated. As a result of theoretical analysis, there is a threshold for the value of the distance between the fulcrum and the brace. When this distance equals the threshold, weighing sensitivity will be zero. Experimental results show that the average linearity is larger than 0.998 and the average relative error between the theoretical weighing sensitivity and the experimental weighing sensitivity is 6.46% within the range of 0~200 grams of force.