The behaviour of galvanized lattice steel structures with joint slip is difficult to model accurately using either theoretical methods or numerical simulations. This paper proposes an accurate and efficient finite element (FE) model for the performance prediction of such structures including the effect of joint slip. In this study, an improved joint-slip model for bolted connections is developed on the basis of experimental results and Ungkurupanian's joint-slip model. Validation of the proposed model is performed utilizing results from full-scale structural testing. Compared with the conventional structural model and the structural model incorporating Ungkurupanian's joint-slip model, the proposed model has the highest accuracy in regard to predicted response. This newly developed model can be readily programmed into existing structural analysis and design software. The proposed model has the potential to improve reliability and safety of lattice structures in practical design.