For predicting detonation velocity (D) and pressure (P) of a polynitro cage compound at its theoretical maximum density with R-P empirical method, it is necessary to modify the term A/3 dealt with the molecular structure in the F factor and to consider the contribution of high crystal density and high strain energy embedded in the molecule stemming from the cage systems to the F factor. Compared with R-P method, the modified R-P one not only preserves original advantages, but also markedly improves the predicting results.With the predicting results of the K-J method taken as the basic data, the relative error of detonation velocities and pressures for all 25 polynitro cage compounds evaluated by using modified R-P method is ±1.9% and ±5.2%,respectively.However,the relative error for the same compounds predicted by R-P method is ±14.0% for D and ±21.4% for P.