The invention provides an idle current detection and calculation method for power network current. Based on the formula iq=A1cos (wt-2m Pi/3), the method is characterized in that a load side power network current detecting part, an idle current resolving part, an idle current scaling factor calculation part and an idle current content calculation part are comprised. The method adopts an instantaneous power calculation method and can quickly detect out the idle current on the load side power network current; based on the detected idle current, in situ reactive compensation can be performed for the power network so as to improve the stability of the power network voltage and reduce the power network wire damage. The detection method is simple and reliable, effectively shortens the development time and cost of a static var generator based on the method, and is conducive to using the market competitive advantage of the SVG control equipment adopting the technology, to stabilizing power network voltage and reducing wire damage, and further to cleaning the power quality of the power network.