The invention belongs to the technical field of bolt pre-tightening devices and discloses a bolt pre-tightening device with the characteristic of high connecting strength. The bolt pre-tightening device comprises a bolt reinforcing assembly, a connecting assembly, a nut locking assembly and a data display assembly. The bolt reinforcing assembly comprises a connecting rod transmission mechanism anda gear transmission mechanism. The gear transmission mechanism serves a retarding mechanism and is used for increasing the torque. The gear transmission mechanism transmits external force to the connecting rod transmission mechanism, so that a cover of the connecting rod transmission mechanism is made to move upwards. The connecting assembly enables the bolt reinforcing assembly to be connected with a bolt on a to-be-pre-tightened assembly, and when the cover moves upwards, the bolt on the to-be-pre-tightened assembly is driven to move upwards. The nut locking assembly enables a nut on the to-be-pre-tightened assembly to be locked and pre-tightened after the bolt on the to-be-pre-tightened assembly moves upwards. The data display assembly is used for detecting and displaying pull force applied on the bolt on the to-be-pre-tightened assembly. By means of the bolt pre-tightening device, the bolt connecting strength is improved on the premise that the strength of a bolt material is unchanged, and the bolt pre-tightening device is applicable to bolt connection of bridges, steel rails and high-pressure and ultrahigh-pressure equipment.