Abstract: The proportional coefficient of horizontal subgrade reaction m is a key parameter to calculate the deformation of retaining wall in excavations using the method for beams on elastic subgrade. However, the range of m value recommended in the existing design codes is quite large and does not consider the effects of soil properties and excavation dimensions. In this study, the differences and deficiencies of m value in different codes are firstly discussed, pointing out that actually m is a simplified parameter for deformation calculation in practice. For excavation, m should be related to the soil properties and excavation width and depth. Through the numerical analyses using HSS model and the appropriate soil parameters, lots of excavation deformation data are obtained by changing the excavation dimensions and void ratio of soils. Then inverse calculation is performed, and an empirical formula for m is proposed. By means of this method, the m values of the soils in 25 excavation projects in Shanghai are determined, and the associated deformations are calculated. The results show that the calculated maximum horizontal displacements of retaining wall are close to the measured ones, with an average error of 2.6%. The proposed method provides an accurate and efficient approach for determining m value for Shanghai clayey soils as well as an important reference for determining m value in other regions.