The design of gear transmission system plays an important role in improving the quality,performance and life of mechanical products.In this paper,the traditional system transformation scheme of main reduction unit of high speed wire roughing mill is studied,and the matching scheme of gear train is explored.The basic constraints of gear train are analyzed,and the speed ratio curves of matching gear and matching gear with different number of teeth are obtained by calculation,and the number of input shaft teeth and gear seat teeth of reducer are determined.The results show that the optimized reducer saves more installation space,the gear layout is more compact and the footprint is smaller than the original scheme.In addition,compared with the original scheme,the number of gears,bearings and couplings is also reduced,so it has more advantages.