A new linear sensing method of deflection and stress, in which the fiber grating bandwidth is stretched by using bilateral cantilever beam, is reported. The theoretical studies and the experimental results show that the bandwidth of fiber grating is sensitive and linear to deflection and lateral force. In the experiments, the range of linear sensing is not less than 17 nm. The sensing sensitivities are 0.658 nm/mm and 5.32 nm/N, respectively.