The invention discloses a reinforced joint structure of an interface between a reactive powder concrete layer and a steel structure layer and a construction method of the reinforced joint structure. The reinforced joint structure mainly aims at solving the technical problem that joints of a reactive powder concrete layer border and a steel structure border are quite prone to cracks under the action of temperature changes due to different materials. According to the technical scheme, the reinforced joint structure is characterized by comprising the reactive powder concrete layer (1), U-shaped steel bars (2) and steel structures (5); longitudinal steel bars (3) and transverse steel bars (7) are arranged in the reactive powder concrete layer (1), left branches (22) and right branches (23) of the U-shaped steel bars (2) are connected and welded to the transverse steel bars (7) in the reactive powder concrete layer (1), steel bar bottom edges (21) of the U-shaped steel bars (2) are connected and welded to the borders of the steel structures (5), the U-shaped steel bars (2) enable the reactive powder concrete layer (1) and the steel structures (5) to be connected into a whole, and the joints of the reactive powder concrete layer (1) and the borders of the steel structures (5) do not generate cracks. The reinforced joint structure is mainly applied to the fields of steel structure bridges and the like.