The equivalent relationship between the spaceborne synthetic aperture radar strict geometry imaging model and the rational polynomial model is derived. By modeling the error propagation characteristics of the whole link, we simulate and evaluate the quantitative relationship among positioning accuracy, image source angle and corresponding point matching accuracy. The theoretical accuracy which heterogeneous stereoscopic positioning can achieve and its superiority are analyzed, and a set of explicit data selection strategies is derived. Correctness of the proposed theory is fully verified by the in-orbit data test, and the error rules under different data combinations are analyzed in detail, which provides a reliable basis for the practical applications of heterogeneous stereoscopic positioning.