The invention relates to a viaduct drainage ditch heating system which comprises a first heating layer, a second heating layer, a third heating layer and a controller. The first heating layer is buried at the bottom of a drainage ditch, the second heating layer is located under the first heating layer, the third heating layer is buried in the side wall of the drainage ditch, and the controller is fixedly mounted on the outer side of a viaduct and electrically connected with the first heating layer, the second heating layer and the third heating layer. The first heating layer, the second heating layer and the third heating layer are additionally arranged in the side wall and the bottom of the drainage ditch, and therefore ice and snow in the drainage ditch can be rapidly and automatically melted in winter, and snow water which is obtained after snow and ice on the viaduct are melted and flows into the drainage ditch is prevented from being frozen again; and melted ice and snow of the viaduct under ice and snow weather are drained in time, safety driving of vehicles on the viaduct is guaranteed, traffic accidents are prevented, and smooth traffic is guaranteed.