In order to study thermal behavior and ablation of insulator in the combustor of gas-generator, the thermo-chemistry ablation model and heat transfer calculation model were established. Considering the fact that the boundary of insulator is moving during the ablation, the models were discredited with predicted-correction method. Coupling calculations were carried out for insulator ablation and temperature field with quasi-Newton method. Temperature of inner wall, ablation velocity and ablation thickness were calculated. The results show that the predicted-correction method and the quasi-Newton method can be applied in unsteady heat transfer and ablation problem with moving boundary.