A simplified model is developed for defective multilayer spectrum simulation in extreme ultraviolet (EUV) lithography. Influence of defect on the reflected light is modeled by phase perturbation and amplitude attenuation of reflection coefficient. An analytical expression of defective multilayer diffraction spectrum is given. In the simplified model, the phase perturbation is dependent on the defect parameters of the 6th layer of the multilayer and the amplitude attenuation is dependent on the bottom defect parameters. Compared to advanced single surface approximation (SSA) model, accuracy of the multilayer spectrum of the simplified model is improved with nearly the same simulation time. The amplitude errors of 0~+3 orders of the multilayer spectrum are decreased more than 50% in 6° incidence angle. The errors are also with little fluctuation in different incidence angles, especially smaller than 12°. The analytical expression of defective multilayer diffraction spectrum is beneficial to analysis the effects of defect to multilayer spectrum and provides the basis for formulation of defective mask correction.