Abstract: The concepts of cloud-rain transform are presented and the four regional radar precipitation estimation equations are proposed. Our research is focused on the expression methods and evaluation criterions of errors of ABS regional radar precipitati on estimation equations. The reason for radar precipitation estimation error is analyzed, and a new data quality control method is proposed to judge erroneous radar-raingauge data pairs through restraining μi,within a reasonable rang. The cloud-rain transform coefficient ABi of a single station is a spatial-temporal function with strong weather and geographic characteristics. The single station misestimate factor μi is given by the relative deviation of ABi to the power of bf-1 from ABS to the power of bf-1, and it reveals that the fundamental cause of precipitation estimation error is the difference between single station observed ABi and the whole region common ABS. Originated from μi,the four other factors describing regional precipitation estimation errors arc defined: the regional average absolute misestimate factor μA,the regional precipitation misestimatc ratio μs and the regional precipitation absolute misestimate ratio μ|s| and the regional average absolute misestimate value EN. The physical meanings of the four factors arc explained and their corrclations are analysed. In the RASIM method, the ABS regional precipitation estimation equation shows the advantage of zero error of regional total precipitation estimation(μs=0) both in theory and prac-tice. The factor μA is the average value of each single station |μA| among the whole region, and can be interpreted as a general expression of coherence and deviation of multiple ABi from ABS. The factoris μA is closely related to the weather system structure and the complexity of its evolution process, however, it is unrelated to the amount of precipitation and incapable to judge precipitation estimation error value. The factors μ|s| and EN are related to both μA and precipitation, and thus they are reasonable and suitable judge criterions for precipitation estimation errors. The experimental evaluations from radars at Wuhan during the four rain events give a value of total ahsolute misestimate ratio μT|S| less than 30%, which is a decrease of 7% compared with that without quality control.