Abstract: Proposed in this paper is an interface element method for coupling multiple subdomains. Based on the general variational principle, it is feasible to formulate the overall stiffness matrix of a coupled structure by assembling the stiffness matrices of subdomains and the stiffness matrix of interface elements, thus being possible to solve the new equilibrium equation to obtain the displacements of each subdomain. The interface element method essentially introduces boundary confinement forces to substructures, and builds up the equilibrium and compatibility on the common boundaries between subdomains. An example of a cantilever beam under uniaxial tension was used to demonstrate the accuracy of the interface element method. In order to apply the interface element method to a substructure hybrid test, the static condensation technique and the BFGS method are further introduced. Only boundary forces and displacement are implemented to realize the coordinating between subdomains, while the common nodes between subdomains are not necessary. Finally, the nonlinear static analysis and the nonlinear time history analysis were conducted on the cantilever beam, which fully demonstrate the feasibility and accuracy of the interface element method.