For studying the influence of impurity absorption on one-dimensional (1D) photonic crystal defect mode, the complex refractive index and Fabry-Perot interferometry are adopted, and variety feature of extinction coefficient with the transmissivity and reflectivity of defect mode in the impurity-doped 1D photonic crystal is calculated. The extinction coefficient has obvious influence on the transmissivity and reflectivity of defect mode. When the extinction coefficient increases from 0 to 0.03, the transmissivity and reflectivity of defect mode change from 1 to 0 and from 0 to 0.86 respectively. The width of defect mode in reflected wave will enlarge when the extinction coefficient increases, while the width of defect mode in transmitted wave turns constant when the extinction coefficient changes.