The solution of diffusion equation in semi-infinite space with photon density wave was considered based on the farther need of experimental model.The corresponding Green funtion was found,and the results of relationship between the flux and uniform absorption coefficients were also obtained.The model is better suited for the research circumstance,this result can be directly used in experiment about image in multiple-scattering media.That is meaning,through to measurement photon flux,the space distribution of variation absorption coefficients can be got by means of matrix inversion.Then the image of object inside multiple scattering media will appear by use of this photon density wave theorgy.