A multiple diffuse reflection (MDR) method is proposed for measuring absorption spectrum of impurity in powder sample. I b has higher sensibiviby than single diffuse reflection method. An absorption spectrum deduced from the MDR spectrum is in good agreement with the absorption spectrum of clear plate sample. In order to verify the resulbs of different refractive index and dispersion, a randomized multiple diffuse reflection computer simulation model was designed to simulate the light beam travelling in the powder layer. The results illustrate that if the particle size is small enough and the dispersion of the meterial is not too high, the only difference between the absorption spectrum of powder sample and the absorption spectrum of clear plate sample is an unknown absorbing optical path. By combination with other measuremente the radiative transition probabilities or intensity parameters can be obtained.