The invention discloses a water-rich stratum metro subsurface tunnel mechanized construction method. The method comprises the crank arm trolley grouting and water stopping stage, the excavating earlysupport linkage stage and the excavating double-rail slag transport stage. Before excavation, a tunnel face is provided with nets in a hanging mode and profile steel, concrete is sprayed so that the tunnel face can be sealed, a multi-directional deep hole grouting trolley is pulled to the working tunnel face, the posture of a crank arm is adjusted, thus, the crank arm conducts drilling and grouting on fixed points on the completely-sealed tunnel face so that soil on the side and the rear portion of the tunnel face can be reinforced; the multi-directional deep hole grouting trolley gets away from the tunnel face, a double-arm multifunctional heading machine is pulled to be located in front of the tunnel face, two arms are used for excavating soil and building a steel grating, and core soilis reserved; and excavated muck enters a muck rail conveying system through a crawler belt arranged in a machine, the muck is transported to a tunnel vertical shaft through a muck truck on rails, a bridge crane lifts the muck to a muck warehouse to be transported, and one cycle of construction is completed. Through the construction method, tunnel water gushing and tunnel mud gushing are effectively avoided, the high construction efficiency is achieved, the risk is greatly reduced, and the construction safety is ensured.