Taking the ground site observation rainfall precipitation as benchmark data,the paper assessed the precision of the latest generation precipitation product 3B42V7 of tropical rainfall observation plan(TRMM) in Laoha river basin in northern semi-arid area. The result shows that the TRMM 3B42V7 in a benchmark Laoha river basin precipitation system is larger, the average deviation is 17.46%, the correlation coefficient is 0.73, the, the precision of satellite daily precipitation is relative high in average sense; But TRMM 3B42V7 absolute deviation reaches 81.26%, the precision of satellite precipitation in an absolute sense is low; After the deviation calibration of month GPCC ground rainfall,the precision of TRMM 3B42V7 on month scale has greatly increased,the absolute deviation is 21.95%, the correlation coefficient is 0.98; The accuracy of TRMM 3B42V7 has obvious correlation with latitude and elevation; TRMM 3B42V7 can better reflect the spatial distribution characteristics of precipitation and precipitation events in Laoha river basin. Therefore,TRMM 3B42V7 can be used for the simulation of monthly scale hydrological process, the evaluation and planning research of water resources in Laoha river basin watershed.