Based on the traditional Doherty power amplifier, a MMIC Doherty power amplifier with high back-off efficiency for 5G communication in N79 band (4.4~5 GHz) was designed in a GaAs heterojunction bipolar transistor (HBT) process. By using cascode structure in Doherty circuit and adding common-base grounding capacitor in cascode structure, the gain and output power of DPA were greatly improved. Lumped elements were used to participate in the matching, which reduced the area of the chip. The simulation results show that in the target frequency band, the gain is greater than 28 dB, the saturation output power is about 38 dBm, the saturation added efficiency (PAE) is 63%, and the efficiency of 7 dB output power back-off is 43%.