Abstract: The PCCP with 4 meter in diameter has been applied in the Beijing to Shijiazhuang reach of the South-to-North Water Diversion Project for the first time since 2006 in China. Based on the safe use of PCCP engineering structure for 100 years, aiming at the technology problems of how to evaluate safety influence on PCCP with broken wires and relaxation of prestressing in the South-to-North Water Diversion Project, the bearing capacity of PCCP has been studied with the methods of actual PCCP test (anti-crack external pressure test with cracks, anti-crack external pressure test with broken wires and anti-crack internal pressure test with relaxation of prestressing) and non-linear finite element numerical simulation funded by the National Scientific and Technological Support Plan and the Nation Natural Science Foundation Project. The results show that the PCCP with a chip or a few small cracks needn′t repair or just need brush cement paste;the PCCP with wide cracks should be repaired according to codes;and the PCCP with a number of vertical cracks or cross cracks and the PCCP with circumferential cracks longer than circumference are judged to be waste pipes. As the main bearing body, the quality of prestressed wires shoud be ensured to avoid broken wires. The impact assessment on PCCP with broken wires should be analyzed with actual test results. Based on the test results and engineer suggestions, and learning from the advanced foreign experiences, the safety assessment of PCCP with cracks has been proposed. The PCCP which does not satisfy the outer surface crack control requirements should be abandoned to meet the security needs (a total of 35 PCCP have been abandoned in this project), and the PCCP which has little cracks is used in the relatively shallow depth region to save the cost of the project. Finally, the next work which is needed to do is described in the paper.