A hybrid electric vehicle (HEV) can utilize the electromechanical path to optimize the ICE operation and implement the regenerative brake, the fuel economy of a vehicle therefore gets improved significantly. Bi-directional Boost converter is usually used in an electric drive system to boost the high voltage (HV) battery voltage to a higher dc-link voltage. The main advantages for a system with Boost converter is that the traction inverter is de-coupled from battery voltage variations causing it to be over-sized. When designing this Boost converter, the switching frequency is a key parameter for the converter design. Higher switching frequency will lead to higher switching loss of power device (IGBT +diode), moreover, it has significant impact on inductor ripple current, HV battery ripple current and input capacitor current. Therefore, the switching frequency is one of the most important parameters for the design and selection of both active and passive components. This paper investigated the switching frequency optimization with consideration of ripple current of input battery, ripple current and thermal stress of input capacitor, inductor and whole converter efficiency. Both the analysis and test results are provided in this paper, which verified that Boost converter with optimized switching frequency could achieve better tradeoff between converter size, cost, and system efficiency.