The inter-turn stator winding fault of synchronous generator, which is common and destructive, greatly affects the security of the generator and the power network. Based on the extended Park vector approach(EPVA), a practical method of reference frame conversion—the extended alpha beta method, was proposed, and the unsymmetric voltage and current caused by the inter-turn stator winding fault in generator was analyzed by this new method. Then the graphical representation and digital characteristic of fault is obtained. This method is reliable and easy to be applied into practice. And it is a noninvasive approach to detect the inter-turn stator winding fault. The dynamic simulative experiment results with different load, demonstrate the effectiveness of the proposed technique. Combined with multi-loop method, this can be applied to the on-line detection and location of inter-turn short circuits in the stator windings of three-phase synchronous generator as a new method. 