The reinforced concrete beam is the main bearing component of building structure, it is of important theoretical meaning and practical value for safety assessment to research the degree of fire damaging for the reinforced concrete structure. According to the experimental standard of the building fire, a damaging test to concrete beam caused by simulated fire high temperature is made, then static load, stress, strain and deflection are measured. The results indicate that rigidity decreases, brittleness increases, the maximum deflection reduces and safety performance of beam declines after fire. The experimental results provide testing proof and calculating methods for residual bearing capacity calculation of concrete constructions after fire.