Normally, the structural fundamental frequency can be got from the vibration tests by means of accelerometers or velocimeters linked with the dynamic signal measuring and analysis system. Based on the principle of reinforcement strain variation synchronized with the structural vibration, the paper introduces a new method to obtain the fundamental frequency of bridge by measuring the environmental dynamic strains of resistance strain gauges bonded on the reinforcing bars of bridge hinge and deck pavement. The real-time strain signals caused by vehicles passed on the bridge were recorded by the dynamic signal measuring and analysis system, and transformed into strain spectrum by fast Fourier transformation in which the fundamental frequency was got. The result was the same as that of velocimeter measuring. Therefore, the bridge fundamental frequency can be simply and accurately measured by the resistance strain gauges.