The high survivability RPR derived from the normal resilient packet ring offsets the low reliability of the single ring.The high survivability RPR network design is difficult to choice parameters without the exact analysis of reliability.so a reliability mathematic model is presented in this paper,which gets a comparatively exact reliability function of the high sur-vivability RPR based on probability and permutation theory and combination theory.The computed results indicate that the reliability of the high survivability RPR is much higher than the single ring’s.