Abstract: Fire deteriorates the performance of reinforced concrete (RC) structures. It proposes a novel method for the nonlinear analysis of RC structures under fire, based on the cellular automata (CA) method and the fiber model of FEM. The CA model is established to simulate the temperature diffusion in the cross section of a RC continuous beam, and then the time-varying temperature in the cross section is evolved. The damage index corresponding to the damage of steel bar has been defined and its variations with time are discussed. Following that, the CA model is coupled with the fiber model of FEM to compile a MATLAB program to analyze the nonlinear performance of RC continuous beam exposed to fire. It can be concluded that the proposed CA model can effectively simulate the diffusion process of temperature in the concrete. Besides, the damage model introduced can quantifies the relationship between the damage of steel bar caused by temperature and heating-up time. Furthermore, the MATLAB program established in the present study can be effectively applied to the nonlinear analysis of RC beams under fire. An effective combination of CA model and fiber model can analyze the time evolution of deflection and bearing capacity of RC beams and evaluate their fire resistance life. Finally, the proposed method can be used as an effective theoretical tool for the life assessment of RC structures under fire.