In this paper, a three-band monopole antenna for hand-held harmonic radar is designed. The antenna is fed by a coplanar waveguide. By loading L-shaped radiating branch on the main radiating body of the monopole antenna and cutting a triangular notch on the ground plane close to the main radiating body, the antenna resonates in three frequency bands: 2.4 GHz, 4.8 GHz and 7.2 GHz. At the same time, a metal baffle is loaded at a distance of 10 mm from the antenna to enhance the directionality of antenna radiation and to receive electromagnetic waves reflected in multiple directions. The size of antenna is 54 mm×53 mm×1.6 mm, and the bandwidth in the three operating frequency bands is 0.51 GHz (2.35-2.86 GHz), 1.39 GHz (4.17-5.56 GHz), 1.46 GHz (6.17-7.63 GHz), respectively. It can effectively cover all the working frequency band of harmonic radar. According to the peak gain and radiation pattern of the antenna, the gain performance and overall radiation performance of the antenna are good in operating frequency band.