Most stroke patients with hemiplegia have difficulty on heel rocker function due to weak dorsiflexors at their paralyzed side. The proposed high-dorsiflexion assistive robotic technology (RT) supports ankle dorsiflexion during gait rehabilitation. Aside from the McKibben-type artificial muscle's contraction to assist swing phase dorsiflexion, a tension spring is aligned in series to support heel rocker function upon heel strike. Because of different requirements of dorsiflexion torque during loading response phase, selection of suitable spring for corresponding user could be important. Springs with either excessively large or small coefficients might the normal heel rocker function. In this research, an identification method based on observing tension on the spring in loading response phase was derived. We aim for simple clinical setting and availability on patients with various pathological gait patterns, especially gait asymmetry. A case study on a stroke patient with hemiplegia was conducted to evaluate effect with the identified spring. Increase of knee angle (before intervention: mean 2.118°, SD 0.418°; during intervention: mean 12.814°, SD 1.764°) and shank angular velocity to the ground (before intervention: mean 117.300°/s, SD 9.491°/s; during intervention: mean 255.875°/s, SD 34.130°/s) indicates sufficient heel rocker function could be supported during intervention of the identified tension spring in this specific case.