A new method of calculating the dynamic accuracy of automatic meteorological station (AMS) is introduced. The computational results of the data observed with two AMS and one meteorological station in Hangzhou show that the standard deviation of the AMS and the meteoro-logical station are appropriate and objective. The computational results of the meteorological station data are approximatly the same as previously assumed values. The standard deviations of AMS are much smaller than the value required by CIMO (Committee of instrument and method of observation of WMO),and satisfy the accuracy requirment of AMS by CIMO.