Abstract: The single pile foundation in marine environment is subjected to long-term cyclic loading due to wind, waves and currents. Under the cyclic loading, the interface shear stress between pile and soft soil and the shear strength of soft soil around the pile will decrease, thus affecting the bearing characteristics of pile foundation. The cyclic interface friction coefficient between Q235 steel and Tianjin coastal soft clay is obtained through the interface shear tests, and the cyclic softening parameters of Tianjin coastal soft clay are obtained through the dynamic triaxial tests, which provides a method to obtain the parameters for quantifying the cyclic friction characteristics of pile-soil interface and the cyclic softening characteristics of soft soil around piles. On this basis, a finite element model for single pile foundation in undrained soft foundation under horizontal cyclic loading is established with the combination of the constitutive model for soft soil, which can consider the strain softening effect of soft soil. The development laws of pile head displacement and reaction response and pile section bending moment under horizontal cyclic loading are studied while the development law of softening area of soil around the pile under cyclic loading is obtained. The calculated results show that the softening area of soil around the pile foundation develops continuously with the increase of cyclic number. Meanwhile, the softening zone of soil has a high degree of development along the depth under the action of high horizontal cyclic displacement. The position corresponding to the maximum bending moment of pile body moves downward.