The moraine dam breach often causes catastrophic floods, this paper designed a field prototype experiment in the Jialongcuo and explored the evolution of the breach floods. Through the analysis of the experiments, the following conclusions are drawn: 1) the process of breach flow can be divided into "initial growth type", "delayed growth type" and "surge type". The first two types can be attributed to the evolution of the breach, and the "surge type" is attributed to the surge caused by the collapse in the upstream. 2) Flow process varies in each stage at different discharge, mainly due to the difference in the rate of undercutting of the breach. 3) A peak discharge formula is proposed involving the erosion of the dam and the influence of the upstream lake catchment, which gives more accurate calculation than the previous formulas.