A novel pattern reconfigurable substrate integrated waveguide (SIW) horn antenna is presented in this paper. By embedding copper posts with ring slots in the middle of SIW and adding PIN diodes as tuning switches, the operating states of the SIW can be electronically controlled. Six SIW H-plane horn antennas are sequentially placed on a circular substrate. Accordingly, the radiation direction of the proposed antenna can be switched by tuning the states of SIW switches, and a 360° beam-steering reconfigurable ability is obtained. Moreover, a printed lens is introduced between the horn aperture and free space for achieving a high gain and good directional radiation patterns. Simulated results illustrate that the proposed antenna is capable of switching the end-fire beam with six identical radiation patterns in the H-plane. Meanwhile, a peak gain improvement around 6 dBi is achieved by employing the printed lens.