A major reason which causes error in the eam measuring is that the measured datum angle is not exactly identical to its designed value. An angle searching method is Put forward in this paper, which adopts only one series of the eam measuring data and use the sectional parabola function for interpolating new series of the "measuring" data at each datum angle. It has been proved, by experiment that the program designed for searching the datum angle in earn measuring is practicable, effective and simple.