The invention relates to a prefabrication and cast-in-place combined utility tunnel construction method. The method comprises the steps that cast-in-place of a bottom plate (1) is conducted, wherein prefabricated laminated side walls (2) are transferred to a site for assembly, and exposed steel reinforcement bars of the lower ends of the laminated side walls (2) and exposed steel reinforcement bars at the two ends of the bottom plate (1) interpenetrate and are fixed; prefabricated top plates (3) are transferred to the site for assembly, the exposed steel reinforcement bars at the two ends of the top plates (3) and the exposed steel reinforcement bars at the upper ends of the laminated side walls (2) interpenetrate and are fixed; the upper ends of the laminated side walls (2) and upper steel reinforcement bars (6) are welded, and diagonal bracing steel reinforcement bars (5) are welded to the inner sides and the outer sides of the steel reinforcement bars at the interpenetrating positions; concrete formworks (7) are cast in place on the inner sides and the outer sides of the steel reinforcement bars at the interpenetrating positions; with a steel reinforcement bar skeleton as a frame body, and in the later cast formation stage, concrete bodies (8) are cast. By means of the method, quick assembly and construction of a utility tunnel can be achieved, the construction efficiency isimproved, the construction joints are reduced, and the under-stress performance and the water-proof performance of the utility tunnel structure are improved.