This paper introduces a optimize design method of ship unloader. The traditional structure design method is totally by experience and manual calculation, while this method is using the Finite Element Analysis (FEA) method to optimize the structure of ship unloader. Therefore this method may keep the stress and deformation of the structure under permission with less use of materials. First we use the FEA analysis software ANSYS to analyze the static strength and stiffness of grab ship unloader, and get its stress and deformation under different work conditions. Then we evaluate the results and modify the structures to improve the performances of the structure under the complex working conditions. Case study shows this method is effective and efficient in practical use.