The utility model discloses an open circuit current load case is prevented to serial -type, including first output, second output and establish ties in proper order a plurality of groups load between the two, parallelly connected switch of every group load, every group load is all including the resistance and the inductance of establishing ties, opening and be closed through the switch, the load case can be controlled and the load value of multiple difference is realized, opening and the closure of any one switch, the load case switching -off state can not appear, the state that can not have disconnection current transformer secondary load in operation process produces, can switch over secondary load under current transformer test condition, test time has been saved, the experiment work volume has been reduced, the current transformer because of experimental work time is shortened, the empirical risk has been reduced, and simultaneously, adopt load transfer mode, the efficiency of the use of single load is improved, components and parts quantity has significantly reduced, the material saving cost.