Objective To quantitatively investigate the cupula time constant in vestibular semicircular canals of human inner ear by numerical simulation and experiment, and to clarify the time process of coding angular motion by semicircular canals. Methods The numerical model of bilateral semicircular canals in human inner ear was constructed, and then biomechanical responses of the cupula were simulated by fluid-structure interaction to calculate the mechanical relaxation time constant of the cupula. Meanwhile, cupula time constant of the volunteers was calculated based on their nystagmus slow-phase velocity obtained in vestibulo-ocular reflex experiment. Results The mechanical relaxation time constant of the cupula calculated by numerical model of semicircular canals in human inner ear was 3.75 s. The average cupula time constant was approximately 4.86 s measured by experiment. The result in numerical model was approximately consistent with that in experiment. Conclusions The cupula time constant in vestibular semicircular canals of human inner ear was approximately 4.86 s, which reflected a combined effect of mechanical relaxation of the cupula and afferent adaptation of semicircular canals, as well as revealed the time process of coding angular motion by semicircular canals.