The invention provides an online monitoring signal transformer suitable for the partial discharge of a high tension switch cabinet. The collected partial discharge signals are transformed into digital signals by the transformer, the digitalized local discharge data are transmitted to a central hub in a wireless mode. The overall power consumption of the transformer is less than 1W, lithium batteries can be used to supply electricity, a complete battery charging can support the transformer to work continuously for more than three months. Additionally the transformer is small in size and light in weight, networking using the mounting method of magnetic absorption is flexible and has very strong anti-interference ability.