The utility model discloses a device for machining a hole series on an engine lathe. A locating mandrel (2) is arranged at the center of a transition connection plate (1), a locating mandrel hole is formed in the center of a rotary disk (3), two T-shaped grooves (10) are symmetrically formed in the transition connection plate (1) through taking the axis of the locating mandrel as the center, a connecting bolt (12) is arranged on the transition connection plate (1), the transition connection plate (1) and the rotary disk (3) are both provided with three indexing holes (11) which are evenly distributed through taking the axis of the locating mandrel as the center, the rotary disk (3) passes through the locating mandrel (2) and is arranged on the transition connecting plate (1), a pressing nut (7) is arranged at the top end of the locating mandrel (2), a locating block (5) and a self-locating block component (8) are symmetrically arranged on the rotary disk (3), and therefore the device for machining the hole series on the engine lathe is wholly formed. By means of the device for machining the hole series on the engine lathe, it is guaranteed that cutting allowance is even in finish machining of the hole system, and the operation is simple and convenient; meanwhile, the machining range of the engine lathe can be enlarged, existing equipment can be fully utilized, and the machining cost is reduced.