The thermal stability of bismaleimide and epoxy modified novolac-type phenolic resin is investigated. Fourier transform infrared spectroscopy results confirm that the phenolic resin is interacted with bismaleimide and epoxy groups. The thermo gravimetric analysis results indicate that the modified resin exhibits better thermal stability than the virgin novolac resin. It is also found that the thermal degradation process can be divided into two stages. The nonisothermal degradation behavior of the modified novolac resin is then studied by multi-stage model-fitting kinetic method and Kissinger-Akahira-Sunose (KAS) model-free method. The two-stage model uses two separated peaks to simulate the DTG curve and the final model predicts the mass loss fraction accurately. It is able to describe the two-stage degradation reaction process and produce two equations corresponding to the two-stage degradation mechanism. The KAS model results in the dependence of activation energy of degradation on mass loss. The activation energy history of degradation also indicates the change of reaction mechanisms.