Structured light projection has been widely used for depth sensing in computer vision. Diffractive optical elements (DOEs) play a crucial role in generating structured light projected onto objects, and spot array is a common projection pattern. However, the primary metrics of the spot array, including density and field of view, are restricted by the principle of diffraction and its calculation. In this paper, a novel, to the best of our knowledge, method is proposed to achieve high-density periodic spot array on a large scale. Further, periodic DOEs, for the first time, are optimized to increase the density of the spot array without decreasing the periods of the DOE. Simulation and experimental results of high-density and large-scale spot array structured light projection are presented, demonstrating the effectiveness of the proposed method.