The invention discloses a tooth-back-cooling-mode-based special tool for helically milling a composite material/titanium alloy. The existing tool has short service life by adopting a bottom cooling mode. The tooth-back-cooling-mode-based special tool for helically milling the composite material/titanium alloy comprises a tool bar, a neck part and a cutting part, wherein the cutting part is connected with the tool bar by virtue of the neck part and consists of four cutter teeth, a cooling hole is arranged on the tooth back of each cutter tooth, four oblique cooling holes are led out from central holes passing through the axis of the tool bar, the aperture of each oblique cooling hole is smaller than that of the central hole, the axis direction directly faces towards the front tool surface of the end cutting edge of the tool, the peripheral cutting edge of the tool and each end cutting edge adopt double tool surfaces of a land, inside cutting edges at the ends of the four cutter teeth pass through the axis of the tool bar and are perpendicular, and three cutting edges are arranged at the end of each cutter tooth. The special tool for helically milling the composite material/titanium alloy can be used for effectively avoiding the plugging of the cooling holes, reducing the wear of the tool, improving the processing quality, prolonging the service life of the tool, increasing the radiation area, restraining the vibration in a cutting process, and decreasing the layering and burring phenomena.