Abstract: Isogeometric analysis (IGA) is a new numerical method developed based on the standard finite element method (FEM) in recent years, which eliminates the geometric error of FEM and has high-order continuity. This paper presents the IGA of three-dimensional structures by using the representation of non-uniform rational B-splines (NURBS) geometry and the applied load and constraints. The simulation results with IGA are compared to those with FEM using linear elements and quadratic elements. Compared to the standard FEM, the advantages of IGA are demonstrated through accuracy and efficiency. A thick-walled cylinder model is chosen as an illustrative example to verify the practicability of IGA. The NURBS elements are applied to the gear and cylinder which have structures with variable sections and need high geometrical accuracy. The results show that the proposed three-dimensional IGA based on NURBS is flexible and applicable for complex three-dimensional structures and the method can generate continuous stress field. The IGA method is expected to be widely used in engineering.