Abstract: The span-wise coherence function of the aerodynamic lifting force in the buffeting response of bridges is analyzed by using the lifting-surface theory of airfoils. Result shows that the values of the coherence function are larger than those of the on- coming span-wise wind velocity fluctuation, and the strip assumption has limitation in some instances. Because the joint acceptance function based on the strip assumption underestimates the response of structures to the wind force, a coherence function for the aerodynamic lifting force along the span-wise direction is proposed , which is fit to be used in the calculation of the joint acceptance function for the buffeting response of bridges.