Based on the Doppler radar data and the data from twenty-seven automatic weather stations from May to June in 2002 and 2003 in the northern and central Fujian,the statistical analysis of optimization is made to obtain the Z-I relation of different regions.The rainfall amounts in precipitation processes in 2005 are estimated.Using variational method and optimum Kalman filter method (combine Kalman Filter with optimum interpolation), radar estimations are tested with rainfall data of Wuyishan Jiuquxi Valley in the northern Fujian.The accuracies for the methods are compared and analyzed.The results show that mean relative errors are less than 25% with variational method and optimum Kalman Filter method,it is also less than 25% from 0 to 100km with optimization method,however,it increase remarkably from 100 to 200km.Mean relative error is the greatest with the relation of Z=300I^1.4.