Taking the 7shafts transmission of an engineering machinery as the research object,the multi-objective optimization research of the transmission is carried out.According to the structure and parameter characteristics of the transmission,the transmission gears are grouped and the mathematical model of optimization is established,which is based on reducing weight,improving the stability and reducing the maximum center distance of shafts.Then the transmission is optimized by using the MATLAB optimization toolbox and optimization results are achieved and verified.The results show that the transmission size and weight are reduced and the stability of the transmission is improved.