The invention discloses an (S)-4-hydroxy-2-oxo-1-pyrrolidineacetamide crystal form I. An X-ray powder diffraction diagram displays X-ray powder diffraction data expressed by the following d value and relative intensity RI value: 7.075 (M), 5.355 (S), 5.092 (S), 4.590 (M), 4.325 (M), 4.259 (S), 4.041 (VS), 3.808 (M), 3.542 (M), 3.445 (M), 3.393 (M), 2.972 (M) and 2.914 (S), wherein VS represents very high strength, S represents high strength, and M represents medium strength. The preparation method of the crystal form comprises the steps of a crude product and crystallization; and acetone and water are used as solvents in the crystallization process. The application effect of the (S)-oxiracetam crystal form I for preparing a medicament for preventing or treating memorial functional disorder is remarkably superior to the medicinal effect of levorotatory oxiracetam; the purity of the crystal form prepared by the preparation method is high and is more than 99.3 percent; and the method has a few adding times of inorganic alkali, and is simpler and more convenient in operation and more favorable for industrialized production and application.