Abstract: The bandgap structure of one-dimensional photonic crystal was calculated and derived with the plane wave method (PWM). The effects of the dielectric constants of high/low refractive films making up one-dimensional photonic crystal structure and filling ratio between thickness of high reflective film and crystal period on the bandwidth of forbidden band gap were analyzed. The function relation between bandwidth and dielectric constants or the function between bandwidth and filling ratio was obtained by least square curve and curved surface fitting to make sure the best value of bandwidth, and to design the periodic structure of one-dimensional photonic crystal. For a one-dimensional photonic crystal with dielectric constants of 13/1 and filling ratio of 0.16, its calculated bandwidth is 0.2564×2πc/Λ and central frequency is 0.3478×2πc/Λ. These results agree with experiment data.