The invention provides a tunnel micro-three-step upper core soil construction method. The tunnel micro-three-step upper core soil construction method comprises the steps that first, an arch advance support is constructed, an upper step arc-shaped pilot tunnel is excavated, and upper core soil is retained and gradually removed with the tunnel surface excavation; second, an advance middle step is excavated, at the same time, a middle step rock-soil body of about 2/3 excavation width of the middle step is excavated, and 1/3 of a following middle step rock pillar is retained; third, a following middle step is excavated, and the following middle step rock pillar is gradually removed; fourth, an advance lower step is excavated, at the same time, a lower step rock-soil body of about 1/3 excavation width of the lower step is excavated, about 1/3 of the rock-soil body in the middle is trimmed into a slope as a passage for machines and equipment, and about 1/3 of a following lower step rock pillar; fifth, a following lower step is excavated, and the following lower step rock pillar and the passage are gradually removed; and sixth, the tunnel bottom is excavated. The construction method effectively controls the deformation and deformation fracture of an initial support system, ensures the safety of tunnel construction, and improves the tunneling efficiency of a tunnel.