This paper presented a 3.1~10.6 GHz ultra-wideband (UWB) low noise amplifier (LNA) in a 0.18 μm CMOS process. The circuit was designed with current-reuse and impedance feedback technology, so it has the characteristics of low power dissipation and flat gain. Simulation results have shown that, across the frequency band of interest, the LNA achieves 17.5 dB of average gain, the input and output return loss is lower than -8 dB, respectively, the minimum NF is about 2.8 dB, and the power dissipation is about 11.35 mW under the power supply of 1.5 V.