In order to solve the limitations of traditional transformer flux restraint technology in electronic transformer application, this paper proposes a flux complex judgment technology for electronic transformer and three-phase transformer. The application situation and the existing problems of flux restraint technology are introduced in transformer differential protection, the influence of transient characteristics of electronic transformer on flux restraint theory is discussed, the problems of angle compensation, inrush current phase selection, trap multiple identification which are used in differential protection of three-phase transformer are researched, and the algorithm implementation process is given. Experiments show that flux restraint theory for electronic transformer can greatly improve the speed of the action of differential protection, and has the reliable identification ability for inrush current.