The inter-turn short circuit fault of wingding is a typical serious fault of the new synchronous condenser,which has a serious impact on the long-term operation of the condenser and the stability of the power grid. In order to ensure the reliable and stable operation of the new synchronous condenser,a method of online diagnosis and location of rotor inter-turn short circuit fault is proposed in this paper. Based on the distortion of the air-gap magnetic field magnetomotive force caused by fault it is deduced that the phenomenon of even harmonic circulation will occur in the same phase and double branches of the stator. Through Fourier decomposition of the branch circulation,the obvious characteristic quantity of harmonics is extracted and analyzed. It is concluded that the characteristic quantity is only related to the spatial position of the rotor where the fault is located,and has nothing to do with the number of fault turns. Therefore,this characteristic quantity can help realize fault diagnosis and location. Based on the TTS-300-2 type synchronous condenser which has been put into use on a large scale,a simulation model is established with the actual condenser in the finite element software while an experiment platform is developed with a condenser simulator for experiments. The simulation and experimental results validate the effectiveness of locating rotor inter turn short circuit faults through branch circulating current harmonics.