The spectrum of fiber Bragg grating(FBG) in inhomogeneous strain fields is distorted due to its inhomogeneity of both the periods and the effective refractive index.The coupling mode theory and Runge-Kuta method can be employed to exactly simulate the spectrum of FBG in such fields,but the convergence speed is slow.On the other hand,although the transfer matrix method could be used instead for higher convergence speed,the precision is poor because of the neglect of the grads of strain change.By improving the FBG equivalent period,a novel simulation method based on modified transfer matrix method is proposed,which has the advantage of quick-convergence as well as good accuracy.