This paper presents a new algorithm, the overlapping averging 4-frame (OAF) algorithm, which can reduce the phase error caused by phase shifter error. The relationship between the accuracy of OAF algorithm and phase shifter errors is given.Based on this relationship, it is verfied that the OAF algorithm can reduce the phase error from phase shifter error. The computer simulation has shown the magnitude of a calibration error and nonlinearity in the phase shifter for a number of different phasemeasurement algorithm has higher accurcy than other phase-measurement algorithms.