A novel multi-legged horse-riding simulation vehicle aiming at providing the equine-assisted therapy is proposed, the functions of which include both transportation and rehabilitation. The whole system consists of a walking system constructed with four identical-legged units, a control system, an energy system, and a riding system. Based on the requirements of the foot trajectory, the configuration of the whole close-chain legged mechanism serving as a legged unit is designed with the structure of a single leg. The kinematics of the legged mechanism is built using the vector loop method, and the dimension is optimized adopting the sequence quadratic program. With the established mathematic model, the form-position inversion method is developed for the fluctuation analysis of the riding platform, and its modified algorithm is proposed according to the walking properties. The closed fluctuating curve group is obtained when the riding platform walks on a treadmill with a constant speed, and two functional curves are selected and analyzed for different walking modes. Combined with the practical requirements of different intensities, the sensitivity analysis is carried out for the reconfigurable process to adjust the fluctuation amplitude. A series of dynamic walking simulations are conducted and analyzed, and a prototype is fabricated to verify the expected functions of the multi-legged riding simulation vehicle. The study provides a new idea and an application reference for equine-assisted therapy system.