The invention discloses an active electricity larceny prevention device and a method aiming at magnetic electricity larceny compensation metering. The device comprises a front-end data collecting module, a signal processing circuit, an electricity larceny behavior judging and identifying module. If behaviors are judged to be electricity larceny behaviors, different treatment measures are adopted according to electricity larceny measures. Especially, when magnetic electricity larceny is performed, compensation metering needs to be performed on the magnetic electricity larceny due to the fact that the magnetic electricity larceny is high in imperceptibility and restores to the normal state when interference is removed so as to facilitate inspection. The steps of the method aiming at magnetic electricity larceny compensation metering is showed in the picture below. By the device and the method, the intelligence level and automation level of the active electricity larceny prevention device are increased greatly, key inspection and evidence obtaining by inspectors are facilitated, and corresponding treatment can be performed timely.