Aiming at fuel-tank overpressure fault occurred in a certain aircraft fuel system ground simulation test,by researching the fuel-tank pressurized principle, the improvement measures in both test-bed system and tested fuel-system were offered, and relevant verifying tests were set up. The verifying test result proves that the unreasonable pipeline designs of the test-bed system and the tested fuel-system were the reasons of the fuel-tank overpressure fault. The improvement measures in tested fuel-system were used in real aircraft fuel system design, which provided guarantee for flight safety