The invention provides a device and a method for processing an inner hole of an air cylinder steel pipe of a pump valve body. A jacking device is additionally arranged, so that when a heavy workpieceis processed on a horizontal lathe, the clamping is convenient, and the stable part size is ensured. The device comprises a steel pipe blank, a jacking plate and an ejector rod; the jacking plate is circular; the jacking plate is connected with the ejector rod in a welding manner; the length of a processed steel pipe is 272.517 MM, the excircle diameter of the processed steel pipe is 134.11 MM, and the internal diameter of the processed steel pipe is 113.03 MM; and the steel pipe is processed by adopting the following steps: material preparing, material sawing, rough turning, finish turning, linear cutting, surface treatment, inspecting, packing and warehousing. The device and the device have the advantages of being convenient to clamp and accurate in processing, ensuring stable part sizeand the like, thereby effectively solving problems and defects in the prior art.