Multi-surface ranging with the use of three dimensional (3D) flash ladar can be useful in accurately discriminating camouflaged targets of interest. In order to estimate multiple surfaces in 3D flash imaging ladar well and truly, a multiple surfaces′ range estimating algorithm in 3D flash imaging ladar via expectation maximization (EM) is proposed. This algorithm can estimate the point spread function of imaging ladar and the target range information simultaneously. Simulation results show that the multiple surfaces′ range estimating algorithm can improve range estimation over traditional mixed Gaussian matching and Wiener filter by up to 70% and 40% respectively.