To realize the noncontact detection of partial discharge of electrical equipment within some range，a wideband，good gain and horizontal plane omnidirectional ultra-high frequency antenna is researched，and it is used as detecting sensor of partial discharge(PD) signals. Characteristic radiation and characteristic impedance of discone antenna are analyzed，and it is found that it is dominant to design the dicone antenna as UHF signal detecting antenna. Then the structure of the antenna is optimized via calculate simulation. The band of the discone antenna is from 200 MHz to above 2 GHz and its average gain is above 4 dB. It is made via discrete method according to the analysis and simulation result，satisfying the design demand. The discone antenna shows good performance to detect analog discharge signals and PD signals in substation from far away. Fixed and mounted PD monitoring system can be developed based on this antenna，and the system can monitor PD of electrical equipment within substation without contacting equipment.