The invention discloses a construction method for an integral straight middle wall type double-arch tunnel. The construction method comprises the following steps that a middle pilot tunnel is excavated according to design requirements, preliminary bracing of the middle pilot tunnel is carried out, the middle wall of a double-arch tunnel is constructed in the middle pilot tunnel, the top of the middle wall is of a Y-shaped structure, a middle wall top cavity is reserved between the top of the middle wall and the top wall of the middle pilot tunnel, a drainage system is arranged on the middle wall, backfill is carried out on the middle wall top cavity, a left hole and a right hole of the double-arch tunnel are excavated according to the design requirements, and pavement construction and tunnel mechanical and electrical installation engineering construction are respectively carried out on the left hole and the right hole after construction. Compared with an identical three-layer combined type straight middle wall structure, a three-layer combined type curved middle wall structure and a five-layer combined type curved middle wall structure, the construction method can effectively reduce the thickness of the middle wall, a structure is simple, construction is convenient, construction cost is reduced, the occupied area of a tunnel outer lead is reduced, and land resources are saved.