Abstract: The seismic response of free spanning submarine pipelines is related to the earthquake input directions. A hydrodynamic force model improved from Morison equation considering excitation directions to analyze the dynamic response of free spanning submarine pipelines under earthquakes is proposed. Motion equations are derived from improved Morison equation on the base of finite element method. Three dimensional FE model is established to simulate the experimental conditions. The numerical results considering sine wave input and simulated El Centro earthquake input are obtained. The comparison of numerical results with experimental results shows that the improved Morison hydrodynamic force model considering excitation directions could satisfactorily predict the dynamic response of free spanning submarine pipelines subjected to earthquakes.