In order to control the prestressed ca ble teｎsile forces and ensure the construction quality, the magnetoelastic me thod was intr oduced to inspect the cable tension in trusses of the new Ｇｕａｎｇｄｏｎｇ Mus eum. Through the comparison between the testing and the design data during different constru ctio n stages, the prestressing loss was estimated and the causes were discussed. At th e same time, the rules of the tension distribution in the single cable and the c able group were obtained. Th e testing results show that there are different degrees of prestressing loss in cables of suspended structure. As an effective and reliable method to measure th e ca ble tension, the magnetoelastic method can provide scientific references for s tructural engineers.