The scanning range and scanning speed of the atomic force microscope are limited by the size of the working stroke and intrinsic frequency of the flexible mechanism; however, it is challenging for the flexible mechanism to account for the large working stroke and high intrinsic frequency in the design to solve the problem. This study proposes a nanopositioning platform based on the bridge-type amplification mechanism and optimizes its configuration and main parameters. First, a new type of double-bridge flexible amplification mechanism is established through the study of the influence of the number and thickness of flexible arms on the intrinsic frequency and amplification ratio of the bridge mechanism. Subsequently, the discretization of the nanopositioning platform is realized based on the matrix displacement method, and the overall stiffness matrix of the nanopositioning platform and the mechanical model of the system are constructed. Finally, the optimization of the main parameters of the flexible amplification mechanism is carried out with respect to the frequency response and the stroke of the nanopositioning platform, and simulation analysis is performed. Finally, the main parameters of the flexible amplification mechanism are optimized for the frequency response and travel of the nanopositioning platform and simulated. The simulation results show that the optimized piezoelectric-driven nanopositioning platform has a first-order intrinsic frequency of 4.4 kHz and a working travel of more than 30 μm×30 μm.