In calibration measurement of RF power sensor, effective efficiency directly measured requires further correction to compensate external power loss. Correction factor is hence introduced, to convert uncorrected effective efficiency to real effective efficiency of power sensor. In conventional calculation method, insertion loss of transmission line connected to sensor is neglected, due to its relatively small value. Yet for higher frequency band, insertion loss undergoes rapid increase. Hence conventional calculation method of correction factor results in an unacceptable calculation error. This paper presents a new calculation method of correction factor, valid for high frequency power measurement. Correction factor increases up to 5% with proposed method applied. Subsequently, an iterative algorithm for correction factor is introduced, achieving precise correction factor results via computer software.