The invention relates to a submarine environment condition simulating device for a diesel engine, which is characterized by comprising an environment simulating chamber, an exhaust back pressure regulating unit, an air inlet temperature regulating unit, an air inlet pressure regulating unit and a cooling water temperature regulating unit, wherein the environment simulating chamber is a gas-tight silo; the exhaust back pressure regulating unit is connected on a smoke exhaust pipeline; the air inlet temperature regulating unit is connected with the output end of the smoke exhaust pipeline; the air inlet pressure regulating unit is connected with the output end of the air inlet temperature regulating unit; the cooling water temperature regulating unit is connected with the cooling water inlet and the cooling water outlet of the diesel engine by a cooling water inlet pipeline and a cooling water outlet pipeline; and the exhaust back pressure regulating unit, the air inlet temperature regulating unit, the air inlet pressure regulating unit and the cooling water temperature regulating unit are controlled by a controller to output values of simulation. The invention can completely simulate the submarine environment conditions for the diesel engine, including environment air temperature, environment air pressure, seawater temperature and exhaust back pressure. The invention provides a base platform for the research and the performance research trial of the submarine diesel engine.