Abstract: An improved algorithm for the atmospheric integral vapor measurement is proposed by using an optimum dual-frequency microwave radiometer. In this algorithm the integral vapor is deduced by detecting the wet delay of the metrical path. The wet delay measurement has high accuracy because the excessive effect of the liquid water in the clouds is eliminated during the detection process. This method could improve the precision of the integral vapor measurement in cloud day. The new method could get a detection error above 35% less than that by the traditional solution using the direct data of the at mospheric radiation brightness temperature.