The invention relates to a method for determining the structure and the thickness of an open-pit-to-underground covering layer, belonging to the field of hard rock mining. The structure and the thickness of an integral descending layer and a flow layer are determined according to the technical requirements of the open-pit-to-underground covering layer, and the structure of the integral descendinglayer is determined by the coarse material and the fine material and the proportions thereof. The flow layer is mainly determined by granularity composition, ingredients and volume ratio. The volume ratio of the fine material is from 15% to 30%, the thickness of the integral descending layer is from 50 m to 30 m, and the minimum thickness of the flow layer is greater than 1.5 times section height; and the total thickness of the covering layer is equal to the sum of the thickness of the integral descending layer and the thickness of the flow layer. According to the determination method of the invention, the rock bust damage of an open-pit-to-underground mine, caused by side slope slumping, can be effectively prevented, the time surface rainfall bursts into underground is effectively retarded, the occurrence possibility of underground mud-rock flow is greatly reduced, air ventilation and air leakage loss is reduced by more than 80%, the temperature exchange between underground and earthsurface in winter can be controlled, and surface cold air is prevented from intruding into underground.