During the bridge service life, the frequency and weight of vehicle loads are increasing with time. By according to time-dependent reliability theory, a Gamma stochastic process based on Monte Carlo simulation is proposed to consider the increasing frequency of load effect, which is used to evaluate structural reliability. Based on the proof load test, by considering the influence of historical load information on present resistance evaluation of bridge structure, the time-dependent reliability equation is modified by setting the coefficient of variation of resistance a time variable. The time-dependent reliability analysis of a reinforced concrete beam bridge is carried out by using the above methods. The results show that: the correlativity of frequency increment does not affect the time-dependent reliability of bridge; the equation proposed in this study can consider the case when the average historical load intensity is between 31.6% and 36.4% of the initial resistance of the structure, which has higher precision to predict bridge reliability. When the load frequency λ is smaller than 10 (1/a) and the inspecting time interval (0,T) is within 35 years, if the historical load intensity is smaller than 29.1% of the initial resistance, the reliability equation based on time-dependent load frequency is available; when the load frequency higher than 2 (1/a) exceeds 36.4% of the bridge initial resistance, and the annual growth rate of frequency exceeds 150%, the reinforced-concrete bridge structure predicted by high degradation function of resistance has higher failure probability within 20 years, which should be paid extra attention. Corrosion resistance of reinforcement should be enhanced during bridge’s design and construction.