Establishing a reasonable interface model for composites and systematically analyzing the fiber debonding process were the key to analyzing the microscopic mechanism of damage and failure in heat resistant C_f/C composite. This study was based on experimental literature reports， considering the submicron scale interfacial transition zone between fiber and matrix， and proposed an interface model that includes fiber， interphase and matrix. The exponential gradient model was used to calibrate the average mechanical properties of the interphase， and the differences between the traditional two-phase and improved three-phase interface treatments were compared and analyzed in predicting the effective elastic properties of the material. The simulation results show that the three-phase model can simulate the overall mechanical response behavior of the material more accurately than that of the two-phase model. Further， the three-phase model was used to simulate single fiber push-out experiment to analyze the effect of interfacial parameters on the progressive debonding process of the fiber. The results indicate that when the release rate of interficial critical fracture energy and cohesive strength are 0.001~0.006 N/mm and 13~33 MPa， respectively， the maximum ejection force of the fiber is positively correlated with these two parameters； beyond this range， the enhancement effect is no longer significant. Increasing the release rate of interficial critical fracture energy or decreasing the cohesive strength can delay the premature occurrence of complete damage at the interface and improve the fracture toughness of the interface. In addition， the cohesive parameters are calibrated by a combined experimental-simulation approach. The analysis results will provide theoretical support for the subsequent multi-scale research on the interfacial damage mechanism of C_f/C composites.