This paper presents the Efficiency Characteristic of Three-Level Converter. Three-Level DC/DC Converter presented in this paper is used a phase shift control with a flying capacitor in the primary side to achieve ZVS(Zero-Voltage-Switching) for the switch. This converter reduces the voltage stress across the main switch to half of input voltage. It shows the main reason of efficiency diminution, comparing of input and output voltage. Also, the loss analysis of each component and the various losses in the circuit are proposed in this paper. The result of the efficiency characteristics are verified using 3kW prototype.