With hourly special persisting rainstorm data from digital weather radar evaluations and gauge observations in the east of Hubei on the 20-22nd,July i n 1998, the characteristics of radar-detecting precipitation calibrated by vari ational method is studied Results prove that the radar estimations calibrated d oes not only keep the distribution condition of the rainfall before calibration, but also the errors from the comparison with gauge observations are improved re markably.