A side vehicle body reinforcing structure may include a center floor panel; a side sill respectively combined to both sides of the center floor panel in a width direction of the vehicle body; a seat cross member configured so that a lower end thereof is combined to the center floor panel and both ends thereof in a width direction of the vehicle body are combined to the side sill to cross the center floor panel in a width direction of the vehicle body; a battery case combined to a lower surface of the center floor panel and disposed at an internal to the side sill; and a partition wall panel respectively both side plates of the battery case in a width direction of the vehicle body, wherein a combining bolt sequentially penetrating the seat cross member and the center floor panel is engaged to the partition wall panel.