The invention discloses a simulator for blocking groundwater seepage by an underground structure, belonging to the technical field of building engineering, and comprising a water tank, a model box, baffles, a phreatic aquifer, an aquiclude, a confined aquifer, a displacement meter and a water level observation pipe, wherein the water tank is connected with a model box, the model box is internally and vertically provided with a plurality of baffles, the phreatic aquifer, the aquiclude and the confined aquifer are sequentially and horizontally paved in the model box from the top down, the displacement meter is vertically installed on the surface of the phreatic aquifer, and the water level observation pipe is vertically embedded in the confined aquifer of the model box and sequentially perforates the phreatic aquifer and the aquiclude. By adopting the invention, groundwater three-dimensional seepage and soil mass deformation condition of the soil mass having the underground structure at each moment can be conveniently and efficiently observed, and real, exact and efficient parameters are provided for the design and the construction by analyzing test results, such as water head change, the ground subsidence distribution and the like, thereby the high efficiency and the safety of an urban underground engineering construction can be ensured.