The invention discloses a construction method of a cast-in-situ prefabricated assembled and combined subway station which is constructed in a foundation pit formed after the excavation and support of a subway foundation pit are completed. The construction method comprises the steps: firstly, placing a bottom plate reinforcing steel bar at the bottom of the foundation pit, arranging dowels on positions, corresponding to a bottom-layer upright post and a bottom-layer side wall, on the bottom plate reinforcing steel bar, and then, pouring bottom plate concrete; secondly, constructing the bottom-layer upright post and the bottom-layer side wall; thirdly, constructing a middle plate; and fourthly, repeating the second and third steps to complete the construction of an upper-layer structure of the subway station, and then, backfilling and earthing a top plate of the subway foundation pit and the part above the top plate, wherein the top plate is a laminated slab, reinforcing steel bars are assembled in the top plate, and reinforcing steel bars are reserved at two ends of the top plate as required.