The shift step must be an accurate value in the traditional algorithm of phase measuring profilometry(PMP) technology.So the software is made to give a chart of error phase in any unequal step phase shifting,and a calibration algorithm is presented to give the correct phase based on this error phase chart.With the help of computer emluator written by us,the calibration algorithm based on checking proved to be correct.So the precise request of phase shifter is reduced greatly.