The circular current in the parallel branches of generator stator winding appears because of inter-turn short-circuit of rotor windings.Up to now， the analysis of the circular current is only qualitative， fault current cannot be calculated accurately.That is why it has limited practical application.The simulation for the inter-turn short-circuit of rotor winding on SDF-9 fault simulation experiment unit is carried out and the current is calculated quantitatively，and the experimental result coincides with the calculated one.Thus the value of the circular current in parallel branches of generator stator winding for different short-circuit turns of rotor winding can be calculated accurately. The protection basis for the inter-turn short-circuit of rotor winding has been provided.