Based on the engineering background of an island water diversion aqueducts truss, this paper put forward a method using prestressed force and outsourcing cement filling material to strengthen the bottom chord of reinforced concrete truss, used the hierarchical load test method to carry out in-situ static load experiment on the strengthened truss, tests deflection, strain(stress) value and their changes of the main control section of truss at different levels of loads, made a comparative analysis of the test results, calculated the value of finite element method, and obtained the mechanical performance of the truss after reinforcement. The experimental results show that the use of prestressed force and outsourcing cement filling material to strengthen truss can improve the bearing capacity of truss structures to a great extent, and new structural layers can work with the original structural layers and their deformation coordination is good. The reinforcement effect is also ideal.