Using mixed coordinate system, this paper presents a strict analytic solution for airborne passive ranging after correctly making variable transformation for Doppler shift equation, which only needs to make two measuring for Doppler shift. As compared to the approximate solution derived from Doppler rate equation, the strict solution applies to arbitrary baseline and its relative calculating error falls as baseline increases. An arrestive speciality is that it can realize a very high positioning accuracy based on lower measurement accuracy for Doppler shift if the space between two detections is close to radial distance of target.