To overcome the shortcomings of the traditional passive-radar-seeker (PRS) for anti-decoy, a complex angle measuring method is proposed in this letter. The complex angle measuring method consists of monopulse angle and spatial spectrum estimation, two angle-measuring units. PRS can get the angle high-resolution features through the complex angle measuring method. To improve the precision and the stabilization of the angle-measure in the active-decoying environment, a grey processing approach is proposed in this paper. The methods of removing gross error and parameter estimation based on the grey entropy definition are proposed in the paper. Using grey data processing approach based on the definitions of grey distance measure and grey relation entropy, eliminate singularity and retain random error. Finally, the simulation results verify the feasibility and anti-decoy capacity of the complex angle-measuring method, and the grey processing approach can improve the precision and stabilization of angle-measurer in active-decoying environment, and can improve the precision of anti-radiation missiles (ARM).