The invention provides a construction method for separating a highway tunnel and a ramp. The construction method comprises the following steps that 1, the separated area of a high hole and a low holeof the tunnel is determined; 2, measurement lofting is carried out in the separated area, and the excavation outline of the high hole and the excavation outline of the low hole are measured separately; 3, the high hole and the low hole are excavated at the same time according to the predetermined footage driving cycle and the determined excavation outlines, and preliminary bracing is constructed after excavation is completed; 4, a plurality of anchor cable assemblies are mounted on the inner side wall, close to the high hole, of the low hole; 5, concrete guard walls are arranged on the two inner side walls of the low hole; 6, the steps from 3 to 5 are cyclically executed until the high hole and the low hole are separated; 7, secondary lining is constructed for the high hole, a high hole concrete floor is laid for the high hole, and a concrete floor is laid for the low hole. The method is convenient and fast for construction, the construction difficulty and construction accident risks are reduced, the work progress is promoted, and the work efficiency is improved.