The invention relates to the technical field of pipe gallery construction, and discloses a construction method for a pipe gallery to down-pass a river channel. The construction method comprises the following steps that S1, steel sheet piles are inserted from one side of the river channel to the opposite side to form a cofferdam until the end part of the cofferdam reaches a set position; S2, waterin the cofferdam is discharged, an installation groove is excavated and formed in the cofferdam, and the pipe gallery is installed in the installation groove until the pipe gallery is close to the endpart of the cofferdam; S3, a waterproof wall is arranged at the end part of the pipe gallery, a transfer weir is formed at the cofferdam through separation, moreover, the end part of the pipe gallery1 is located in the transfer weir, and the steel sheet piles not involved in the transfer weir are removed; S4: the steel sheet piles are inserted from the transfer weir to the opposite side to formthe next cofferdam until the end part of the next cofferdam is located at the next set position, the steel sheet piles at the end part of the last cofferdam are removed, and the step 2 and the step 3are performed; and S5, the step 4 is repeated until the pipe gallery is installed to the opposite side. According to the construction method, the problems of poor applicability of a flow division method, environmental damage of a phased soil cofferdam method and high cost of a pipe jacking construction method are effectively solved.