The invention discloses a diesel engine aftertreatment device. The diesel engine aftertreatment device comprises a catalyzing silencer and a supercharger connected with the catalyzing silencer through an exhaust pipe; the exhaust pipe comprises a mixing pipe, a first bend and a back straight pipe; the mixing pipe is located at the middle portion of the exhaust pipe, a mixing core is embedded into the mixing pipe to form a mixing device, the length of the mixing pipe is larger than the diameter of the mixing pipe by 2.5 times, and a spraying nozzle is arranged on the pipe wall of the mixing pipe in an inclined manner; the first bend is downwards bent, the supercharger is connected with the mixing pipe through the first bend, a corrugation section is arranged between the first bend and the supercharger, the bending radius of the first bend is larger than the diameter of the mixing pipe, and the diameter of the first bend and the diameter of the mixing pipe are coincident; and the back straight pipe is vertically arranged at one end of the catalyzing silencer, and is connected with the mixing pipe, the length of the back straight pipe is larger than the diameter of the mixing pipe by 2 times, and the diameter of the back straight pipe is coincident with the diameter of the mixing pipe. By means of the device, the urea anti-crystallizing capacity is improved.