Abstract: The similarities and differences between the proper orthogonal decomposition (POD) and the mode superposition method (MSM) are studied not only in principles but also in applications. According to the principles of POD and MSM, comparative studies are made theoretically. The similarities and differences are illustrated in their respective applications, with two random fields of the fluctuating wind loads and the corresponding fluctuating wind-induced responses of a hyperboloidal cooling tower as examples, obtained from wind tunnel tests and the dynamic calculations in the time-domain. Both POD and MSM are methods used for the decomposition and reconstruction of a random field by linear superpositions of the spatial modes and corresponding time coordinates. However, their application fields are quite different: the POD is always used for the analysis of known load fields but the MSM is for the calculation of unknown response fields. Furthermore, the extraction methods of the spatial modes and the corresponding time coordinates for the POD and the MSM are different, as well as their mathematical and physical meanings and their contributions to the original random fields. The spatial modes of the POD and the MSM are both orthotropic, but while the time coordinates of the POD are orthotropic, those of the MSM are not. Consequently, the sum of the POD eigenvalues reflects the whole energy of the original random field, but it is not the case for the MSM due to the coupling between different modes.