According to the structural characteristics and operation mode of the safety mechanism of the Three Gorges ship lift, the influence factors of the clearance of the thread pair of the safety mechanism are analyzed. The safety mechanism is affected by the installation and manufacturing error of the equipment, the clearance of the mechanical transmission system, the structural deformation and deformation caused by the external load and the wear of the operating parts of the equipment. The maximum change value of the theoretical clearance can reach ± 49 mm, and the maximum value in actual operation does not exceed ± 15 mm. Based on the sensing detection technology, the clearance detection scheme of the safety mechanism of the Three Gorges ship lift is proposed. The scheme can realize the real-time detection and early warning of the clearance of the safety mechanism, and avoid the excessive load of the clearance detection device, the accuracy of device requirements were meets through the gap test, and the scheme has guiding significance for engineering practice.