Objective To study the effects of radiation sensitivity coefficient, frequency of treatment and mature age of tumor cells on therapeutic efficacy by numerical simulation. Methods A hybrid mathematical model for the growth of solid tumor under radiotherapy was established, with considering the influence of both tumor microenvironment (including oxygen, extracellular matrix and matrix-degrading enzymes) and tumor activities (including proliferation, apoptosis and adhesion) on tumor growth. The linear quadratic model was also introduced to depict tumor response to radiotherapy. The progresses of tumor growth under different conditions were simulated to assess the therapeutic efficacy. Results The therapeutic efficacy was better when the radiation sensitivity coefficient and mature age of tumor cells increased. When the total amount of the radiation dose was the same, the effects of treatments seemed no difference either with high frequency or low frequency. Conclusions The simulation results are consistent with the clinical results, which can provide a new method for the theoretical and clinical research on tumor radiotherapy.