A spatial light modulator based on a metamaterial structure and a preparation method thereof. The spatial light modulator includes an array of optical function elements and a control circuit. The optical function element includes a metamaterial structure formed by a metal nanostructure layer and a metal reflector layer, with a medium layer and nonmetal conducting material layer being provided between the metal nanostructure layer and the metal reflector layer. The spatial light modulator is simple in structure, high in integration, easy in manufacture and low in cost. Furthermore, the spatial light modulator is capable of high-speed modulation, the depth of modulation is controlled easily, and a low drive voltage may be obtained.