Based on rigorous coupling theory，the influence of the dispersion of the core，cladding，film and surrounding material on the dual-peak resonance effect is studied. The result shows that the theoretical model which considers both the core and cladding material dispersion is necessary and feasible. Further，the influence of the material dispersion on the transmission characteristics of LPFG is analyzed for different film parameters. The deviation value between the dual resonant peaks is calculated before and after considering the material dispersion. The result shows that the deviation value is 1.5—2 nm and 6.5—7.5 nm, respectively. Finally，the influence of the material dispersion on the sensor sensitivity is studied for the dual-peak LPFG sensor. The result indicates that the minimum resolution for the film refractive index is 10-8，and the contour line figure after considering the material dispersion supplies accurate parameter combinations in the design of this kind of sensor.