Abstract: MICAPS data,Doppler radar data and NCEP data,etc.,were used to analysis characteristics and causes of the MCC in a short time flooding rainstorm occurred on July 25,2013 in the Loess Plateau. The results showed that: 300hPa synoptic scale anticyclonic,500hPa synoptic scale southwesterly airstream is direct weather influence system of the MCC in the upper-middle troposphere,700hPa α- mesoscale transversal shear and 850hPa α- mesoscale low vortex on the west side of subtropical high is direct weather influence system of the MCC in the lower troposphere; the low-value tongue of moist enthalpy field at surface is one of the trigger mechanism of MCC; the high value center of moist enthalpy field which is greater than or equal to 40 ℃ corresponding to the MCC generating area; the formation and maintenance of southwest low level jet,the generating and maintaining of adverse wind convergence region,with low-level convergence and high level strong divergence configuration appeared on the radial velocity field in MCC generating area provide dynamical condition for the generation of MCC and formation of the heavy rain; the space allocation of cold and warm advection created favorable conditions for the generation and eastward development of MCC; the high-value zone of moist helicity in space cross- section diagram has indicative significance for the generation,development and eastward movement of MCC.