Abstract: Paper first introduces the basic principles of the Simultaneous Iterative Reconstruction method(SIRT). Then the effective of the SIRT method is discussed by doing the numerical model experiment of four velocity models. Finally, the shortest path method is adopted to do forward modeling and an inversion image of a nuclear power plant CT data of crosshole acoustic wave in karst area is applied by using the SIRT method, which, as a result, shows the possible location of the caves.