The invention discloses a small frequency scanning horn antenna based on microstrip array feed, so as to solve the problem that the size of a high-gain horn antenna in the prior art is over large. An upper dielectric substrate is embedded at the bottom port of the horn antenna; a radiant floor is located between the upper dielectric substrate and a lower dielectric substrate; a patch array is etched on the upper surface of the upper dielectric substrate; a feed network is etched on the lower surface of the lower dielectric substrate and is connected with a coaxial feed connector arranged on the side surface; and a microstrip array is formed on the whole. The patch array is formed by sub arrays with different sizes corresponding to different working frequencies. Through using the microstrip array to replace a rectangular waveguide to feed the horn structure, on the premise of ensuring the same gain, the size of the horn antenna can be effectively reduced, the scanning effects of a radiation pattern at different frequencies are realized at the same time, the view point of the antenna is expanded, functions of miniaturization, multi-frequency beam scanning and the like are effectively realized, and the small frequency scanning horn antenna based on microstrip array feed of the invention is applicable to the field such as wireless communication.