The designing process and measurement results of a 220 GHz frequency doubler based on monolithic GaAs Schottky barrier diode are introduced. Multi-anode structure is adopted in this frequency doubler to improve the output power. Eight anodes are mirror symmetrically arranged along the waveguide to form balanced structure. The conversion efficiency and operating bandwidth are improved by adopting various junction capacitances to suppress the difference of scattering parameters among wave ports. The designed frequency doubler is fabricated and measured. Measurement result shows that the conversion efficiency of frequency doubler is above 15% from 204 GHz to 234 GHz and a peak output power of 90.5 mW with conversion efficiency above 20% is demonstrated at 226 GHz. Finally, a 220 GHz frequency doubler with high output power, high conversion efficiency and wide operating bandwidth is realized by adopting multi-anode structure.