Based on the the transfer matrix method,the propagation of electromagnetic wave in the one-dimensional photonic crystal is deduced,and the dispersion relation of photonic crystals and the reflection characteristic curve are calculated,and the relationship between reflection characteristics and the structural parameters are analyzed.The variation and the reflection spectrum of defective one-dimensional photonic band gap are shown by computer simulation.The simulation and calculation of photonic crystal sensor are conducted for measurements of height and refractive index of liquid.This provides a theoretical basis for the practical application of defective one-dimensional photonic crystal sensor in liquid measurement.