In order to accurately calculate the damage probability of directional energetic KE-rod warhead to tactical ballistic missile (TBM) and complete combat effectiveness evaluation of warhead, on the basis of the analysis of the big error rate and low accuracy of traditional damage probability calculation method, the damage energy of the kinetic rod was divided into the energy generated by the shock wave, residual kinetic energy of rod and the chemical energy of energetic material, and the damage probability calculation model based on energy ratio was established. Under the assumption, the paper choosed M39 missile as TBM target to calculate damage probability. The results verified the rationality and credibility of the model, and it provided a method and technical means for damage probability calculation.