The invention relates to a mechanical main shaft with four output heads. The main shaft comprises a casing, an input shaft, an input shaft gland, a large spiral gear, four output main shafts, small end covers and small spiral gears, wherein the input shaft is pivoted on the casing through a deep groove ball bearing and an angular contact ball bearing; the input shaft gland is arranged on the input shaft in a sleeving manner and arranged on the casing; the large spiral gear is arranged on the input shaft and driven by the input shaft; the four output main shafts are distributed in a crossed form; each output main shaft is pivoted on the casing through a single-row radial ball bearing and another angular contact ball bearing; the small spiral gear is arranged on one end of each output shaft and meshed with the large spiral gear; the small end cover is arranged on each output main shaft in a sleeving manner and arranged on the casing. The mechanical main shaft with the four output heads, disclosed by the invention, has the advantages of convenience in use, high machining efficiency, multifunction and the like, and can achieve the composite machining functions of milling and drilling wood materials by mounting different categories of tools, and the like.