The invention discloses a diesel engine tail gas composite noise reduction device. The diesel engine tail gas composite noise reduction device comprises a catalytic oxidation device body, a particle trapping device body and an exhaust silencer, wherein the particle trapping device body is fixed to the exhaust end of the catalytic oxidation device body and used for adsorbing and filtering PM particles, and the exhaust silencer is fixed to the exhaust end of the particle trapping device body. The catalytic oxidation device body comprises a first shell body and a purification catalyst carrier. The particle trapping device body comprises a second shell body and a honeycomb-shaped ceramic carrier. The exhaust silencer comprises a third shell body and a stepped diameter changing exhaust pipe. The stepped diameter changing exhaust pipe comprises a first-order exhaust pipe, a second-order exhaust pipe and a third-order exhaust pipe which are arranged in an inserting mode, and the diameter of the first-order exhaust pipe, the diameter of the second-order exhaust pipe and the diameter of the third-order exhaust pipe sequentially become smaller. According to the diesel engine tail gas composite noise reduction device, the structure is compact, and space utilization is reasonable; not only can tail gas be filtered and purified, but also multi-frequency noise can be well eliminated; the effect that tail gas purification and noise reduction are conducted together is achieved, the structure is simple, the cost is low, the service life is long, assembling and disassembling are facilitated, and the tail gas purification efficiency and the noise elimination efficiency are high.