Aluminium alloy members under axial force have broad application in structural field. Owing to low elastic modulus, aluminium alloy members are easier buckling than steel members. Based on the reasonable and equivalent calculation model and the related calculation formulas of rotational restraint stiffness kφ, lateral restraint stiffness kx, and distortional buckling critical half-wave length λ that provided by lipped channel web plate to flange under longitudinal distribution stress, the distortional buckling load calculation formula of the lipped channel is derived combining the thin-walled bar buckling theory in elastic medium. The distortional buckling loads and distortional buckling critical half-wave lengths at the different wall thickness have been calculated using the calculation formulas of this paper, and the results have been comparatived with the finite strip method. The comparison results show that: the average ratio of caculation results from formulas of this paper and results from CUFSM is 0.997and0.971 respectively,the corresponding variance is 2.9*10-5and 7.5*10-5. So the calculation results of this paper is in good agreement with the finite strip software, the calculation formula of this paper has enough calculation precision and good stability. At the same time, the calculation results of this paper is more concise than calculation formula for the same type, easy to be applied, may be used in practical applications and taken account into design codes and guidelines.