Microstrip patch antenna has been widely used in communication, radar and other fields because of its many advantages. Reduction RCS without affecting its radiation performance has been an important research direction to improve its radar stealth performance. By analyzing the RCS Reduction Mechanism of microstrip antenna, a method of loading H-shaped slot on rectangular microstrip antenna is proposed to improve its radar stealth performance. On the premise of less influence on antenna radiation performance, the RCS of antenna is greatly reduced in X-band.