As global warming,more extreme events occurs than before,once it occurs,and it causes serious influence, so it become more and more important to research meteorology disaster, it not only can help us know disaster,conduct disaster forecast and loss assessment, but also it benefit for solving problems for government. Using a hydrological model named floodarea with a module for simulation. Based on land-use, runoff coefficient value, roughness value of Yangzhi ditch, the paper researched the results of simulated data of runoff depth and cumulative precipitation. It revealed the relation and calculate critical rainfalls triggering mudflow in different water-level using floodarea model. The results showed that: 1) The trend of precipitation and temperature is -0.02,0.032 ℃/a in 5 year moving average, respectively. 2)The relationship of data-fitting depth and accumulative precipitation in six hours is better than other period of time in Yangzhi ditch. 3)Based on fitting results, the paper put forward the risk precipitation in different grades at the warning spots.