AC excitation motors offer advantages such as constant frequency under variable speed and decoupled power in steady-state operation, making them suitable for applications like pumped storage and flywheel energy storage. However, these applications demand rapid emergency braking under high-inertia loads, which traditional mechanical braking strategies fail to meet. This study proposes a flexible braking strategy and parameter optimization method for high-inertia AC excitation motors. First, based on rotor structural characteristics, the strategy connects the rotor to a DC excitation source and the stator to multi-stage resistors, and derives the equivalent braking circuit. Second, a braking parameter optimization model is established, with multi-stage braking resistance, rotor excitation current, and resistor switching speed as variables; motor ratings and resistor power limits serve as constraints; and the shortest braking time is set as the objective. The model is solved using a genetic algorithm. Finally, multi-stage resistance braking results and influencing factors are analyzed via Matlab/Simulink simulations, and a 7 kW AC excitation motor platform is used to verify the simulations. Results show that the proposed multi-stage flexible braking strategy effectively reduces braking time, and optimized parameters achieve minimal braking duration while satisfying system power constraints, balancing braking efficiency and device economy.