A spacer grid of a nuclear fuel assembly having a simple shape structure is proposed. The spacer grid includes square grid cells having respective inner walls and constituting a square lattice structure. Each of the grid cells includes a plurality of springs for elastically supporting a fuel rod. Each of the plurality of the springs has a fixed end along a vertical direction on each of the inner walls and a free end curvedly provided in a horizontal direction from the fixed end. The grid cells also include a plurality of flow channels each provided in the vertical direction to each of the grid cells and a plurality of mixing vanes each protrudingly provided in a downstream direction of cooling water flow at end parts of each of the grid cells.