Under the action of Taft ground motion records, the dynamic nonlinear time history analysis of the reinforced concrete frame structure were carried out. The earthquake demands of the reinforced concrete frame structure were given, the importance index of each random variable was obtained by variance importance analysis method of this reinforced concrete frame structure which was solved by Monte Carlo numerical simulation method. The results show that: The importance sorting of random variables, such as yield strength, damping ratio and structural quality was ahead and elasticity modulus of concrete was in the end for most earthquake demands. When analyzing the earthquake demand of reinforced concrete frame structure, we can consider the influence of several random variables, such as the yield strength of steel bar, the damping ratio and the structural quality. The calculation and analysis above may be helpful for improving the calculation efficiency of the analysis of earthquake demands.