The utility model provides a bridge bottom surface crack detection device, which relates to the technical field of crack detection, and comprises a bridge body, an arc plate is arranged on one side wall of the bridge body, an arc plate is fixed on one side wall of the arc plate, a convex plate is arranged on one side of the arc plate, a cylinder is arranged below the arc plate, and the convex plate is fixed on the other side wall of the arc plate. The top of the cylinder is fixedly connected with the protruding plate, a groove is formed in the surface of the cylinder, a gear is arranged in the groove, an arc-shaped toothed plate is fixed to the bottom of the arc-shaped plate, a fixing plate is fixed to one end of the cylinder, and cameras are fixedly installed at the top of the fixing plate at equal intervals. The driving motor drives the gear to rotate, at the moment, the gear is meshed with the arc-shaped toothed plate, the cylinder moves, the cylinder moves to drive the fixing plate to move, the fixing plate moves to drive the camera to move, the effect of conveniently carrying out camera shooting detection on the bottom face of the bridge body can be achieved, and therefore the effect of improving the detection safety can be achieved.