Compared with the traditional single-mode fiber Bragg Grating(FBG) sensor, the few-mode FBG sensor is less susceptible to the influence of external independent parameters, and has better precision. However, there is no corresponding theoretical basis for the design of grating parameters. For this problem, based on FBG coupled mode theory, the reflection spectrum of the few-mode FBG with LP01 mode and LP11 mode in the fiber core is simulated and analyzed by using OptiGrating and Matlab software. The simulation results show that the reflection spectrum of the few-mode FBG has a three peaks structure which is different from the single peak structure of the traditional single-mode FBG. The changes of grating period, grating length and refractive index modulation depth will have a regular effect on the reflectivity and central wavelength of each peak.