This article presents a nonlinear parametric model of force amplification ratio and an electromechanical model to couple the deformable frame with the piezoelectric stack in order to promote high-efficiency energy harvesting from human walking locomotion. Two improved frames (Frames I and II) are developed based on the modeling and simulation results. The experiments verified these modeling and simulation results that improved frames demonstrate a higher amplification ratio (8.4 for Frame II and 8.0 for Frame I), in comparison to the original frame (3.5). The experiments also verified these results that under the simulated walking excitation (100N, ~1.4Hz), the piezoelectric stack coupled with Frame II produces 4.1mJ energy during each step, higher than the stand-alone stack (0.16mJ) and the stack with the original frame (0.64mJ). Note that the energy conversion efficiency of Frame II (9.1%) is even lower than that of Frame I (10.7%) and the stand-alone stack (25.8%). As such, this article concludes that the energy output of the piezoelectric stack depends largely on the frame deformations in terms of seven coupled frame parameters, instead of only one frame parameter (tilt angle), as commonly used in the referenced literature.