The utility model provides a reinforcing and seepage preventing structure for a pressure diversion tunnel. The reinforcing and seepage preventing structure for the pressure diversion tunnel comprises an original lining concrete layer, a reinforcing and seepage preventing layer, grout stop rings and grouting layers, wherein the reinforcing and seepage preventing layer is arranged on the original lining concrete layer, the grout stop rings are arranged between the original lining concrete layer and the reinforcing and seepage preventing layer, a space between the original lining concrete layer and the reinforcing and seepage preventing layer is divided into a plurality of grouting areas by the grout stop rings, and the grouting areas defined by the original lining concrete layer, the reinforcing and seepage preventing layer and the grout stop rings are filled with the grouting layers. The reinforcing and seepage preventing structure for the pressure diversion tunnel has the advantages that if a pressure diversion tunnel with a small diameter ranging from 3 m to 5 m has many wide longitudinal fractures and large in seepage amount or serious in reinforcement bar corrosion, the water flow cross section is only reduced by 2% to 3% and even less after reinforcement and seepage prevention are carried out, and according to the reinforcing and seepage preventing structure and a construction method of the reinforcing and seepage preventing structure, the structure is simple, steps are reasonable, safety is high, and the structure and the method have good practical value on a built pressure diversion tunnel.