This paper presents the design and verification of a piezoelectric energy harvester with compound two-stage force amplification frame and compact footprint size to achieve high power output for a piezoelectric stack. An improved design of the conventional bridge-type force amplification frame is proposed with compound beam, which is able to maintain the large force amplification ratio while bearing a large loading force. Analytical model is developed based on Euler-Bernoulli beam theory to predict the force amplification ratio of the compound two-stage force amplifier. The architectural parameters are optimally tuned to achieve the largest force amplification ratio, so as to obtain the maximum power output for the piezoelectric stack under other constraints. Simulation study is carried out by finite element analysis to demonstrate the advantage of the proposed compound two-stage force amplifier over conventional design. Moreover, a prototype harvester is fabricated for experimental testing. Results indicate that the proposed harvester features high safety factor, large amplification ratio, and compact size, which can be adopted in practical application for scavenging energy induced by human footstep during walking.