Ankle-Foot-Orthosis (AFO) is usually applied on affected leg of stroke patient with abnormal muscle tone. AFOs are usually made by thermoplastic material which cannot sustain prolonged mechanical force. Thus while walking with thermoplastic AFO, it could correct gait, but at the same time it would usually break down within several months' usage. However, there were few studies concerning the test of AFOs. The purpose of this study was to develop a method for testing AFOs with cyclic walking and then validated its performance. A walking robot was designed as testing apparatus, which comprises foot, ankle joint and lower leg. The foot of robot could wear an AFO and is flexible on loading. Ankle joint of robot was constructed with 2 degrees of freedom (DOF) passive motions. Lower leg of robot was assembled with two servo motors and one linear actuator, which could drive leg and foot walking on the sagittal plane with 3-DOF. Four springs were selected to provide various stiffness for the ankle joint of robot, according to patient's abnormal muscle tone. After loading gait data of one subject to robot as the target gait data, the robot would simulate his/her walking pattern including kinetics and kinematics behaviors. We analyzed 90 steps of the robot cyclic walking on a forceplate. The root mean square accuracy ± mean standard deviations of vertical ground reaction force, tilting angle of foot, and angle of ankle joint were 80.5N ± 9.5N, 1.9degree ± 0.5degree and 2.1degree ± 0.3degree, respectively, as compared to the target gait data. The walking robot showed good repeatability during walking, with low standard deviations as 1.3%, 0.8% and 1.8% of full scale respectively. In conclusion, the robot developed is a reliable tool for testing AFOs.