There was a rare rainstorm weather process in the North of China on July 21，2012，which led to the most severe flooding disasters．The weather system of the process was the cold front with the upper trough，but such a system would not lead to more than 200 mm rainfall in 24 hours according to the statistical results of the last decade ( 2000 － 2011) ． After the precipitation in Beijing ，the torrential rain occurred in the middle of Hebei Province ( Langfang and the northeast of Baoding) ，where heavy rainfall occurred relatively less in the past． Thus，some reasons of the torrential rainfall in Hebei and the forecasting focus were analyzed in the article，based on the conventional observation data，reanalysis data from NCEP at 1° × 1° spatial resolution，regional automatic meteorological observation data and Doppler weather radar data． The comparative study of weather patterns，physics conditions and meso － and micro－ scale systems were carried out with another rainstorm process which occurred on the 24th July 2011． The results show that there were great differences between two weather processes in extreme value of precipitation and rainfall area，although their precipitation efficiency and meso － and micro － scale systems which directly resulted  in two precipitation processes were similar under the same synoptic scale circulation situation ( low － cold front type) ． The extreme precipitation in 7． 21 process had a closely relation to strong moisture transport，intense dynamic condition and high precipitation efficiency，but the train effect for 6 hours was the leading cause of the heavy rainfall． The configuration of low frontal zone of se and low － level jet on the south of shear line led to the train effect in the middle of Hebei Province，which was concluded as a forecast point of the kind heavy rain events． And，the ground mesoscale convergence line ahead of the cold front was a key point for accurately forecasting heavy rainfall area，which was better than based on the southeast quadrant of the lower vortex，because strong precipitation occurred along with lines．