In order to verify the influence of different damages on the lateral distribution law of load in prefabricated multi-girder bridges and explore a bridge damage identification method based on the lateral distribution law, the influences of joint damage degree, local damage degree of girder, damage location, and damage area length are considered. The rigid joint plate beam method is used to study the lateral distribution law of load in prefabricated multi girder bridges under joint and girder damage conditions. The results indicate that the transverse distribution influence line of the girder on both sides after joint damage intersects with the influence line before damage. The impact line of a damaged girder decreases overall. The smaller the residual stiffness coefficient, the closer the damage location is to the mid span, and the larger the damage range, the greater the degree of decrease. When the girder and joint damage occur simultaneously, the analysis can be conducted by comparing the impact line with the sensitive beam when damaged separately. Based on the variation law of the lateral distribution influence line of the sensitive girder before and after damage, the damage category of the bridge can be identified, while the specific damage location cannot be identified.