Due to its advantages of low ripple in inductor current, excellent electromagnetic compatibility, and reduced stress on power devices, the three-level flying capacitor Boost converter(FCBC) has found widespread application in photovoltaic and energy storage fields. As voltage levels increase, ensuring balanced voltage stress on power devices becomes particularly important. This paper conducts an in-depth study on voltage stress balancing issues in different application scenarios and corresponding balancing strategies are proposed. Additionally, the paper provides detailed modeling of the voltage stress on switch during the turn-off process with the corresponding oscillation suppression snubber circuit. Finally, a 120kW prototype with two parallel FCBCs was built to verify the analyses and solutions.