The invention discloses a bridge safety detection system based on a cloud platform. The system comprises a bearing acquisition module, a traffic volume detection module, an environment temperature acquisition module, a river parameter acquisition module, a parameter influence scheduling processing module, an additional load capacity analysis module, a crack image acquisition module, a crack processing module, a crack evolution construction module, a management server, an early warning deduction module and a bridge safety supervision terminal. According to the invention, the additional trafficdanger influence coefficient, the temperature change rate and the river environment destroy influence coefficient are obtained according to the traffic volume of vehicles on the bridge floor, the environmental parameters and the river parameters; crack change influence coefficients of various influence factors of the bridge on cracks on the bridge is comprehensively analyzed; and the predicted passing early warning time is counted through the crack threshold value, so that the accuracy of crack evolution statistics is improved, the time and energy required for manually checking cracks are saved, the accuracy of the predicted passing early warning time statistics is improved, and the safety of vehicles or personnel passing through a bridge can be improved.