In this paper, we present a method that unlike-pair interactions are determinated by explosive detonation data. The unlike-pair interaction parameters kN2-H2O= 1.03, kN2-CO2= 1.035, kH 2O-CO2= 0.96 are deduced from the calculated results of explosive RX-23-AB,HNB and PETN with our statistical mechanical chemical equilibrium code CHEQ-like. At the same time, the theoretical Hugoniots of explosive PBX9404 are calculated with these parameters. The results in better agreement with the experimental data show that the parameters and method are reliable.