The invention discloses a static mixer for an automobile exhaust duct. The static mixer comprises a pipe body, fins and a nozzle. The static mixer is characterized in that: the nozzle is arranged on the pipe body, the sections of the fins are 'V'-shaped, and a plurality of fins with different lengths is alternately and radically arranged in the pipe body. Gas disturbance can be effectively increased by adopting the 'V'-shaped fins, so that waste gas and urea are in full turbulent mixing through the mixer, achieve relatively high uniformity before entering a selective catalytic reduction (SCR)catalyst and further are fully reacted to reduce the NOx content of the automobile exhaust. The fins with different lengths are arranged across, so that different structures of the fins can be used for strengthening disturbance, and pressure drop caused by the middle material part can be reduced. By calculation and analysis of FIR special design software of automatic vehicle location (AVL), the mixer of the structure has good mixing effect and low exhaust back pressure, and fulfills the purposes of fully mixing the jet urea and the jet tail gas without generating high pressure drop.