This paper presents a 12-18 GHz Low Noise Amplifier(LNA) Monolithic Microwave Integrated Circuit(MMIC) in GaAs process, and the design of this LNA layout is verified in ADS EM simulation. This LNA circuit uses single DC power supply. In the design of matching network, the minimum noise matching design, conjugate matching technology and the negative feedback structure are utilized to meet the requirement of low noise, gain flatness and power output. The simulation indicates that in the band of 12-18 GHz, the Noise Figure(NF) of LNA varies from 1.15 dB to 1.41 dB, and power transmission gain is 27.9-29.1 dB, the 1 dB compression power point is 15 dBm, and the Voltage Standing Wave Ratio(VSWR) of input and output is less than 1.72.