Underground space subsurface excavation construction method adopting combined roof

The invention provides an underground space subsurface excavation construction method adopting a combined roof, which comprises steps: a proposed underground space is divided into a plurality of spaced channels, first metal plates which are higher than the top ends of the channels are arranged above space positions of the adjacent channels through a traction method, pipe joints which are provided with embedded grouting pipes are arranged in the channels through a pipe jacking method, metal frame units are arranged on top plates of the pipe joints, waterstop coating is injected between the top plates of the pipe joints and the first metal plates through the embedded grouting pipes, adjacent side plates of the pipe joints arranged on adjacent channels and soil bodies between adjacent side plates are removed, the top plates which are arranged on the pipe joints of the adjacent channels are connected through second metal plates, support units are arranged in the channels, concrete is casted in the top plates of the pipe joints, reinforced concrete is casted on bottom plates of the pipe joints, and reinforced concrete is casted on the side plates of the pipe joints which are arranged on the channels of the two sides of the underground space. The underground space subsurface excavation construction method adopting the combined roof reduces construction cost, guarantees construction quality, and is simple in construction method and rapid in construction efficiency.