The utility model provides a device for machining long, thin and multiple holes of an engine rocker arm shaft. the other end of the balance supporting plate which can be fixedly connected with a fluted disc seat clamped with a machine tool is movably connected with a tip seat; wherein the fluted disc seat is provided with a clamping fluted disc for clamping a machined part, the tip seat is provided with an adjusting pad for balancing the machined part, the fluted disc seat and the tip seat are respectively provided with a top hole for clamping the machined part, and the tip seat is provided with a hollow tip which longitudinally penetrates through and can be inserted into a machining tool. When in use, a workpiece is clamped and fixed; Due to the fact that the arrangement of the balance supporting plate, the clamping fluted disc, the adjusting pad and the like is adopted, the formed whole body can achieve the micro balance effect on long and thin multi-hole machining of the machined part, and the long and thin hole deviation phenomenon caused by gravity center change easily occurring in the drilling machining process can be overcome.