With the rapid development of urban railway, more and more bridge structures have a tendency to combine highway and railway to ease the congestion of urban traffic, which brings challenges to the detection and load test of the combined highway and railway bridge. We introduced the calculation method of load test control of Chongqing Qiansimen Jialing River Bridge, obtained the theoretical control results of load test under different working conditions, including internal force, deformation, frequency, mode and so on, and compared the results with measured results of load test, and thus evaluated the actual carrying capacity of the bridge accurately. We also systematically studied the calculation and evaluation of load test of combined highway and railway steeltruss cable-stayed bridges and gave specific guidance methods which would provide references for the same type of bridge load test in the future.