A side vehicle body reinforcing structure is provided to improve efficiency of load transferring and performance against a vehicle collision. The structure includes a center floor panel that forms a bottom surface of a vehicle body and a battery case coupled to a lower surface of the panel. A side sill is coupled with both sides of the panel in a width direction to be disposed at both sides of the battery case, and has a cross-section formed in a box shape and extends in a front and rear direction of a vehicle body. A seat cross member has a lower end coupled with the panel, and crosses the panel in a width direction to be coupled with the side sill. A pipe nut extends vertically to sequentially penetrate the battery case, the side sill, the panel, and the seat cross member and is fixed to the battery case.