Abstract: Reinforced concrete (RC) rectangular liquid-storage tanks, which are broadly used to reserve rinsing, sewerage, petroleum and chemical liquid, etc., are mainly applied to such corporations as water-supply and drainage, sewerage-disposal, petroleum and chemical industries, railway and so on. In the seismic response analysis of these structures, dynamic fluid pressure is one of the earthquake actions with extraordinary importance. In this paper, supposing that the liquid in liquid-storage tank is ideal, no revolved and no compressible, and ignoring the influence of surface gravity wave, and adopting the liquid-structure interaction model of no sloshing rectangular liquid-storage tanks, and aiming at the bidirection-wall RC rectangle liquid-storage tanks with elastic walls, the velocity potential function of liquid movement is expressed as overlapping of the velocity potential functions between the side direction deformation and rigid body movement, and so the dynamic fluid pressure calculation formulas are derived. For the convenience of engineering application, considering the literatures in existence and writing MATLAB programs, the simplified calculating formulas of dynamic fluid pressure under the action of horizontal earthquake actions are acquired, and the coefficients of dynamic fluid pressure are tabulated, and so the theory calculation base is provided for the subsequent engineering design about these structures.