The invention discloses an in-service bridge support damage diagnosis method based on a vehicle braking effect, and belongs to the technical field of bridge support damage diagnosis. The objective ofthe invention is to solve the problems that an existing in-service bridge support damage diagnosis method cannot accurately perform structural damage positioning and is not high in measurement precision. According to the invention, the accurate bridge finite element model is established by using a model correction method, and a vehicle brake numerical simulation method is provided, so that a braketest scheme suitable for the bridge to be detected can be formulated more accurately. A proper wavelet basis function decomposition level is selected by utilizing a cost function, wavelet packet decomposition is performed on a free attenuation signal acquired at the pier top of the pier, and a damage index is constructed to diagnose the damage position and degree of the support. The method is simple to operate, economical and practical, has certain robustness and noise immunity, and does not greatly influence the bridge structure.