The invention provides a bolt pre-tightening force detection method. The method is based on the bolt connection stiffness theory, and the bolt pre-tightening force detection is achieved by a bolt pre-tightening force agent model correction method. The specific implementation process can be divided into three steps: firstly, based on the actual characteristics of a bolt connection structure of a tested structure, establishing a connection stiffness model of a bolt pre-tightening force and a bolt joint surface; secondly, calculating a law of function of the bolt pre-tightening force on a modal parameter based on the connection stiffness model, and establishing a bolt pre-tightening force agent model based on a neural network; and finally, correcting the bolt pre-tightening force agent modelbased on an artificial fish swarm optimization algorithm to realize the bolt pre-tightening force detection. The bolt pre-tightening force detection method provided by the invention is based on the influence law of function of the bolt pre-tightening force on the stiffness of the bolt joint surface, the sensitivity characteristic of the modal parameter to the connection stiffness is fully considered, the detection of the bolt pre-tightening force is achieved based on the change of the connection stiffness, and the bolt pre-tightening force detection method has the ability of positioning and quantitatively evaluating the degree of change of the pre-tightening force of the bolt with a changed pre-tightening force from a plurality of bolts.