The invention discloses a machining method for an engine water pipe. The machining method comprises the steps that firstly, first-time finish turning is conducted, a water pipe blank is clamped on a first-procedure clamp, and then the water pipe blank is subjected to turning; secondly, second-time finish turning is conducted, the water pipe blank subjected to the first-time finish turning is clamped on a second-procedure clamp, and then the water pipe blank is subjected to turning; and thirdly, third-time finish turning is conducted, the water pipe blank subjected to the second-time finish turning is clamped on a third-procedure clamp, and then the water pipe blank is subjected to thread turning. According to the machining method for the engine water pipe, the water pipe blank is clamped through the special clamps, and the clamping operation is made to be convenient and easy; and meanwhile the clamping reliability is high, the clamping precision is high, the machining efficiency of the engine water pipe is improved, and the production cost is saved.