With the development of wireless communication technology and satellite navigation technology, passive positioning technology has become a hot topic in the field of electronic countermeasures. This paper mainly analyzes the passive positioning technology, focuses on the analysis of the theory of passive direction finding and proposes the algorithm of orientation and geometric union. Through the ground detection system to verify the algorithm, the absolute error of the target radiation source is 1.16°×10-4 on the longitude and 1.104×10-4 on the latitude, the relative error is 9.77×10-7 on the longitude and 3.23×10-6 on the latitude. The actual error distance is 26.67 m calculated by MATLAB. Through experimental verification and result analysis, the algorithm is effective and feasible for nontimed target radiation sources.