The invention relates to a mobile device for detecting local discharging of electric equipment of a substation, and a positioning method. The detecting device is mounted on mobile equipment and is composed of an antenna matrix, an ultra high-speed data sampling unit and a data processing unit. The positioning method comprises the following steps: using an ultra-high frequency (UHF) antenna to receive an ultra-high frequency electromagnetic wave generated by to-be-detected local discharging of the electric equipment of the substation; after performing amplifying and filtering treatment on the ultra-high frequency electromagnetic wave by a prepositioned broadband amplifier, synchronously sampling by virtue of the ultra high-speed data sampling unit, sending to the data processing unit and performing data processing on a four-way signal; and displaying the position of a local discharging source and early warning information on a display screen. The detecting device and positioning method provided by the invention can be used for thoroughly detecting and positioning the local discharging of all equipment in the substation; the detecting cost of the local discharging of the equipment in the substation is greatly lowered; the defects can be early found while the substation is subjected to routing inspection; power-off accidents are reduced, thereby increasing the intelligent level of the substation; and the detecting device and the positioning method have the characteristics of low cost and high efficiency and can quickly detect and position the local discharging of the whole to-be-detected substation.