The invention discloses a method and a system for dynamically identifying vehicle axle load, wheelbase and speed by means of a reaction force. The method comprises the steps of arranging a dynamic identifying module on a body structure, and acquiring reaction force data by means of the dynamic identifying module when a vehicle passes by a body structure; performing calculation on the reaction force data which are acquired by the dynamic identifying module for obtaining the reaction force and a reaction force time history; identifying an abrupt change which corresponds with a vehicle axle through a time history curve which corresponds with the reaction force time history, acquiring the number of vehicle axles, and time points of each vehicle axle in driving on and leaving the body structure; calculating a reaction force nominal value and the vehicle speed through the time points in driving on and leaving the body structure and the reaction force time history; and respectively calculating the vehicle axle load and the wheelbase through the reaction force nominal value and the vehicle speed. The method and the system realize a function of identifying the vehicle axle load, the wheelbase and the speed by means of one system. Not only can weighing of the vehicle in low-speed driving be realized, but also weighing on the vehicle in high-speed driving can be realized. The method and the system have advantages of simple structure, high convenience in mounting, relatively high identification precision and relatively high stability.