A 77 GHz power amplifier based on a 0.13 μm SiGe process was presented. A two-way combined structure was used to increase the output power, and a two-stage differential structure was used to increase the gain. The cascode structure was selected for the power stage to improve the output impedance and facilitate the matching. The structure of common emitter stage with neutralizing capacitor was selected for the drive stage to increase the gain. Two pairs of differential signals were obtained from the input through the Balun power divider of two-way coupled lines, which were amplified by two channels, and were output by the combination of Balun power combiner of two-way coupled lines. Transformer matching was adopted for inter-stage matching. The proposed power amplifier was simulated by the ADS software. Simulation results showed that the small signal gain was 19.6 dB, the peak power additional efficiency was 11%, and the saturated output power was 18.5 dBm at 77 GHz.