Abstract: For the effect of de-ambiguity and accuracy due on amplitude-phase errors in Watson-Watt direction finder, the invalidity reason of de-ambiguity rule is analyzed. A method called all phase calibration for the output of reference channel is proposed. By this method, optimal phase correction value is gained which is used to process phase shift for the output of reference channel. Thus, the phase relationship between the output of direction finding channels and reference channel meets the requirement of the rule of de-ambiguity. The robust of de-ambiguity is improved. Through the analysis of characteristics of direction finding errors, errors express for phase errors between direction finding channels is given. Then, the fitting coefficients of errors curve can be estimated by least square method. Omnibearing errors calibration can be realized by error measured data in a given area by this method and direction finding accuracy can be improved. Simulation results prove the validity of the proposed method.