Abstract: The stability problem is a key concern for the performance of C-section purlins under wind loading. Aiming at this problem, a semi-analytical model is proposed for predicting the longitudinal stresses of simply supported C-section purlins considering both lateral and rotational restraints by sheeting. Formulae used to calculate the longitudinal stresses of the roof purlins are derived by using the classical bending theory of the thin-walled beams. To validate the accuracy of the present model, a comparison is made between the analytical results data obtained from software Maple and the test data from related literatures. It is shown that the results calculated from the proposed model agree well with the data from these two methods. Thereafter, the parameter analyses on the stress and displacement are conducted, and the effects of lateral and rotational stiffness on the limit states are investigated. The results also shows that the bracing restraint can change the buckling mode of purlins. The model proposed can be used to calculate the longitudinal stresses distribution and displacement of simply supported purlins under uplift loadings.