Abstract: The frequency analysis of age difference (Δt) between the results of zircon U-Pb dating and whole rock Rb-Sr dating for 32 granite plutons shows that the Δt displays a symmetrical normal distribution (skewness C sk=0.36; kurtosis C ku=2.99) in the histogram. The Δt is both positive and negative, with a mean of 2.08 Ma, and the percentage of age difference is less than 5% (absolute value). Using least squares regression procedure, a best regression equation with high correlation coefficient (r=0.998) and regression coefficient close to 1 (a=1.003) is fitted to the points of the zircon U-Pb ages and the whole rock Rb-Sr ages for 32 granite plutons. These statistic characteristics indicate that the zircon U-Pb dating ages are corresponding with the whole-rock Rb-Sr isochron ages for granites as a whole. The whole-rock Rb-Sr isochron dating method for granites is mature and reliable. the zircon U-Pb age cannot represent the emplacement ages of granites, but the crystallization age.