A new serial-fed omnidirectional slot array antenna is proposed. Eight annular slots are etched back to back on both sides of the stripline, and a Y-shaped slot is loaded inside the slot to extend the length of the Y-shaped slot. The top is etched with horizontal grooves to form the final Y-T slot structure to improve the unit radiation performance. Genetic algorithm (GA) is used to further optimize the array so that its working bandwidth is further widened and the gain is improved. According to the design results, the antenna samples are fabricated. The actual measurement shows that the impedance bandwidth |S11|<-10 dB of the antenna is 7.93% (5.56~6.02 GHz), and the peak gain in the bandwidth is higher than 8.99 dBi. Operating at 5.8 GHz, the E-plane sidelobe level is lower than -10.11 dB, the peak gain is 9.43 dBi, and it has stable omnidirectional radiation performance.