Abstract: Based on potential energy method, a preliminary study of elastic lateral distortional buckling (LDB) and restrained distortional buckling (RDB) of I-beams is presented. Since the existing potential energy expressions of LDB of I-beams cannot reflect the effect of transverse distributed load, a new expression of total potential energy is first derived by using nonlinear elastic theory. The proposed expression is equivalent to the classic potential expression when the distortion of web is suppressed, and accounts for the combined actions of several common loads, such as transverse distributed load, concentrated vertical load and end moments, when the web is flexible. Then, according to the proposed potential energy expression, a RDB equation for continuous composite beams is deduced after some simplifications. Both the simplifications and RDB equations are verified by finite element method. The results of the present study have important theoretical and practical significances, and provide a rational basis for the practical design methods.