This paper proposed a new method for evaluation of cavitation erosion in hydraulics based on CFD (Computational Fluid Dynamics) and experiment. A simulation model is made, which has same geometry of a submerged jet experiment system. According to the analysis of flow and pressure distribution characteristics from CFD and the erosion map in experiment, it is found that die erosion has close relationship with the distribution of cavitation number σ which is calculated from flow and pressure. The relation makes possible that with only calculating the distribution of σ on surface of specimen by CFD, the erosion risk can be evaluated. Erosion map for different jet distance are predicted with the method, and they fit well with erosion experiment results.