Abstract: Based on the old design transformation requirements, in this paper, taking the MHB5t semi-gantry crane after changing the span as the research object, the three-dimensional solid model of the whole machine structure is established through AutoCAD, and ANSYS Workbench finite element software is used to check the structure under three kinds of limit working conditions. It is concluded that when the trolley is in the beam span, the maximum stress is 75 MPa, and the total deformation of the crane is 8.26 mm; while when the trolley is directly above the steel leg, the maximum stress is 35 MPa; and when the trolley is at the end of the cantilever, the maximum stress is 53.8 MPa, and the total deformation of the crane is 12.48 mm; All of them meet the requirements of the specification. In summary, the semi-gantry crane with 2.3m span can meet the design requirements.