The invention provides a leaching agent for oil-containing drilling cuttings and oil-containing drilling wastes and a using method of the leaching agent. The leaching agent comprises, by volume, 80-100 parts of polyoxymethylene dimethyl ether, 0-20 parts of methyl tertiary butyl ether and 0-20 parts of petroleum ether. The using method of the leaching agent 20 parts by volume. The application method of the leaching agent comprises the steps of mixing the oil-containing drilling cuttings and/or the oil-containing drilling wastes with the leaching agent in a stirrer; stirring the mixture at a certain shearing rate for a certain period of time for leaching, standing to be subjected to solid phase natural sedimentation; and carrying out solid-liquid separation, and obtaining the oil-containingdrilling cuttings and/or the oil-containing drilling wastes subjected to deoiling treatment. According to the leaching agent for the oil-containing drilling cuttings and the oil-containing drillingwastes, the processing steps of the oil-containing drilling cuttings or the oil-containing drilling wastes can be simplified, and the processing cost can be reduced; after the oil-containing drillingcuttings or the oil-containing drilling wastes are processed, the oily substance content can be effectively reduced, and the oil-containing drilling cuttings of the oil-containing drilling waste scanreach the emission standard; and the leaching agent and emulsified diesel oil recovered by fractional distillation can be recycled, and the circulating utilization rate of the oil-based drilling fluidand the leaching agent is greatly improved.