Boost converter is used to boost the high voltage (HV) battery voltage to a higher dc-link voltage in some HEV traction inverter applications. The main advantages for the system with Boost converter are: 1) using the boost converter, traction inverter is de-coupled from battery voltage fluctuations causing it to be over-sized, 2) with higher dc-link voltage, traction inverter could achieve higher torque capability for motor especially at high speed condition. When designing this Boost converter, the switching frequency is a key parameter for the converter design. Switching frequency is directly related to the power loss (specifically switching loss) of IGBTs of a Boost converter. Moreover, it will also change the converter operation, causing different inductor ripple current, input battery ripple current as well as input capacitor ripple current. Therefore, the selection of switching frequency is very important to the performance 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, voltage overshoot during IGBT turn-off, inductor and whole converter efficiency. Both the analysis and test results are provided in this paper, which verify that Boost converter with optimized switching frequency could achieve better tradeoff between converter size, cost, and system efficiency.