Earthquake induces serious damage to the social infrastructures, such as harbor. Owing to the deadly earthquakes, several cases of damage in port and harbor structures are reported worldwide historically. To reduce the earthquake induced damage of quay wall, seismic design method has been evolving till nowadays. Due to its uncertainty and complicity, seismic design of the quay wall is a difficult problem. Research efforts on the quay wall have been focused on the revision of design codes. However, complex interactions in the quay wall system were not reflected in the design codes.The quay wall system consists of the followings: quay wall structure, water, soil, and earthquake. During an earthquake, components of the quay wall system interacts with each other. This interaction is called fluid-soil-structure-interaction (FSSI). In previous studies, deformation of soil and quay wall structure appeared to be affected by FSSI effect. Hence, understanding the behavior of port and harbor structures is important for a safe seismic design.However, previous studies have not focused on two major problems related to the behavior of quay wall. Firstly, deformation characteristics of soil and quay wall structure regarding the FSSI have not been evaluated extensively. Although several experiments and numerical modelings were conducted to evaluate the behavior of quay wall, a lack of its experimental cases and insufficient evaluation has hindered the comprehensive understanding of dynamic behavior of quay wall. In previous studies, the analysis of the experimental cases were done by simply observing reponses during the earthquake at each respective location, but not by evaluating relationships between them. Secondly, difference of behavior of quay wall, according to the condition of surrounding soil is not clear. In the field, reinforcement techniques such as densification, soil compaction pile (SCP), and deep cement mixing (DCM) are often employed on the foundation soil. However, understanding of behavior of quay wall constructed on the foundation soil, on which reinforcement technics are employed, is insufficient. Due to the difficulties in simulating the remediation of soil in physical modeling, the majority of previous studies were done only in simple models, consisting of a quay wall structure and sand.For a better understanding of the behavior mechanism of gravity-type quay wall, following two subjects are discussed in this study. Firstly, mechanism of dynamic behavior of gravity-type quay wall are evaluated. Investigation of the frequency characteristics of the quay wall and understanding its behavior regarding the EPWP, liquefaction, and fluid-soil–structure interaction are aimed to enlighten the behavior mechanism. Secondly, comparison of behavior of quay wall with different subsoil conditions (untreated, densified, DCM reinforced) are conducted. Deformation characteristics of quay wall was evaluated as the way in which quay walls dissipate energy during a shake. In each test models with different subsoil conditions, the stiffness of sliding and rocking along with the way in which energy is dissipated is discussed. Moreover, a more beneficial reinforcement method for subsoil, between densifying and utilizing DCM, for constructing a quay wall is proposed.