This brief presents a fast and energy-efficient level shifter with wide conversion range. To achieve both energy-efficient and high-speed voltage level conversion, a novel architecture combined with multi-threshold CMOS technique is employed in the proposed circuit. A mixed-threshold current mirror circuit is proposed to solve the reduced swing issue in the prior arts. Moreover, auxiliary bias circuits are inserted to guarantee that the low-threshold pull down networks could be strongly cut off while in leaking state. As a result, the power consumption would be reduced to a great extent. Measurement results based on SMIC 55-nm MTCMOS process demonstrate that the proposed level shifter could provide robust voltage conversion from 0.12V to 1.2V. At the target voltage of 0.3V, the proposed level shifter shows a propagation delay of 17.86ns, a static power of 73.95pW, and an energy per transition of 26.59fJ for input frequency of 1MHz.