A novel omnidirectional partial discharge (PD) ultra-high frequency (UHF) antenna sensor is designed based on the microstrip antenna theory. In order to extend the operation bandwidth, the meandering technology is used to modify the structure of microstrip antenna. The genetic algorithm method is used to obtain the optimal parameter of modified structure, which makes operation bandwidth reach to the widest. The operation bandwidth of modified microstrip antenna is 450~2800MHz, which covers the mainly frequency range of PD UHF signal. Meanwhile, this antenna is also advanced for small size, omnidirectional measurement, high antenna gain and high sensitivity. The simulated insulation defect PD test results show that this antenna can detect the typical PD UHF signal effectively and meet the requirement of PD detection in substation.