Based on the mathematical model of altimetric compensating of lifting weight of single arm crane,a general structure form is obtained by solving and analysis,and combining transmission mode of differential reducer to achieve the lifting and luffing process of single arm crane with one reducer. On this foundation,the change of the height of lifting weight in the luffing process of the system is analyzed by simulation of ADAMS/cable,and comparing with the results of MATLAB mathematical model,the design of the differential reducer is proved to meet the actual needs of the project.