The semicircular canals,composed of lateral,anterior and posterior canals in the inner ear,are the sensors of equilibrium during head rotation movements in the three-dimensional space.Semicircular canals are filled with endolymph confined by the cupula.The study of the relationship between endolymph flow and cupular deformation is important in revealing the semicircular canals biomechanical behavior.To date,there are few studies focusing on the transient endolymph flow and cupular deformation in response to a head rotation motion.The lateral semicircular canal is mainly responsible for the sense of the horizontal rotation movement.In order to figure out the intricate dynamics in the lateral semicircular canal during the head rotation motion,the time evolutions of both endolymph flow and cupular deformation are analyzed in this article by using a fully coupled fluid-structure interaction model.It is shown that the cupular deformation provides cues for understanding the physiology of sensing the head rotation.