The invention discloses a power conversion device and a voltage control method. The power conversion device includes a first stage circuit configured to generate a first output voltage, a second stage circuit configured to receive the first output voltage and generate an output current and a second output voltage, and a control unit configured to control the first stage circuit according to a set value of the output current, thereby adjusting the first output voltage. The invention can be adapted to a wide range load voltage by adjusting the first output voltage of the first stage circuit according to the set value of the output current of the second stage circuit.