Aimed at the break process of earth-rock dam of complicated change of water dynamics condition and strong water soil couple effect and combined with reservoir flood regulation, clear water scouring and mechanics of breach erosion invasion,this paper set up a physically based numerical model to simulate the overtopping break process of earth dam on the base of breach model.This model was applied to the simulation of break process of JP reservoir dam,and reproduced the flood flow process of dam-break,breach width and progression process and verified the rationality and application potential of the model.