Abstract: In order to solve the problem of insufficient lifting capacity of the blowout preventer (BOP) handling system installed on rig, In the case of no overall replacement of the device, the differences of its original design rules were studied and analyzed. A new secondary tension unit (STU) was designed and installed, and the operation was coordinated with the original BOP handling system. It effectively solves the major defect of the original BOP handling system and the actual use effect is good. Generally used as a device for tensioning BOPs, the STU can play a more important role in some special operational situations through its functional expansion.