The invention belongs to the technical field of solar cells and provides an organic solar cell having a cascaded metal grating structure. The organic solar cell comprises a conductive film layer, a hole transport lay, a uniform absorbing layer, a grating layer and a back cathode, which are arranged from top to bottom; the grating layer is a one-dimensional periodic structure formed by arranging aplurality of cascaded gratings with the same structure transversely; each of the cascaded gratings includes a first grating, a second grating, a third grating, and a fourth grating which have the equal period and are arranged in sequence, wherein the grating ridge widths W1, W2, W3, and W4 of the first grating, the second grating, the third grating, and the fourth grating are sequentially increased, and the grating ridge heights of the first grating, the second grating, the third grating, and the fourth grating are equal. The invention improves the absorption efficiency of the solar cell and realizes broad spectrum absorption.