For quantitative evaluation of fire endurance, this paper presented a prediction method on the fire endurance of post installed rebar beams exposed to elevated temperature. It was based on equivalent section method, which regarded initial sections as ladder sections by strength reduction of concrete and reinforcement under high temperature. The simplified calculation theory about the mechanical properties of members at ambient temperature and the calculation formula of the ultimate strength of single anchored rebar in fire were used. The feasibility of the theoretical calculation was evaluated through a comparison between the results obtained by the prediction method and the experimental measurements. The results showed that the fire endurance calculated by formula agreed well with the test data with the error of 15%, equivalent to about 15 mins. It was feasible to use this method to predict the fire endurance.