The invention discloses a multi-process step machining combined machine tool for tappet holes of an engine, which comprises a bed body, wherein a cylinder body feeding workbench is arranged at the lower side part of the bed body; a guide rail in the up and down direction is arranged on the bed body, a headstock which can move up and down is mounted on the guide rail, a row of expanding and boring cutters corresponding to the tappet holes of cylinder bodies, a row of boring and reaming cutters corresponding to the tappet holes of cylinder bodies and a row of honing cutters corresponding to the tappet holes of cylinder bodies are sequentially mounted at the lower part of the headstock, and a headstock lifting device is mounted on the bed body; and machining positioning devices are respectively arranged on the cylinder body feeding workbench corresponding to the expanding and boring machining stations and the boring and reaming machining stations. By adopting the multi-process step machining combined machine tool, the traditional machining process is improved, and the machining quality is greatly improved; the tappet holes of three cylinder bodies can be simultaneously machined, and the machining efficiency can be greatly improved; and the expanding and boring machining precision and the boring and reaming machining precision can be further improved by arranging the machining positioning devices.