A system and method for controlling a start of a fuel cell vehicle are provided. The method includes supplying hydrogen and air to a fuel cell and operating a converter so that a voltage on a high-voltage bus is constant, wherein the converter is disposed between a high-voltage battery and the high-voltage bus which is connected to an output terminal of the fuel cell. The voltage on the high-voltage bus is maintained at a preset lowest control voltage and the voltage on the high-voltage bus is adjusted based on a result comparing a preset lower-limit operational voltage of an inverter with an inverter detection voltage. The inverter is disposed between the high-voltage bus and a drive motor, and the inverter detection voltage is detected on a terminal of the inverter which is connected to the high-voltage bus.