In order to accurately detect the inter-harmonic parameters， an inter-harmonic detection method based on stochastic subspace identification（SSI） and stabilization diagram is proposed. The SSI can detect system parameters directly according to the measured data which contains system information. First， the number of inter-harmonic components and the order of the model are tested by use of the stabilization diagram， and then the actual frequency of each inter-harmonic in the original noisy signal is accurately detected by SSI algorithm. If the signal-to-noise ratio of the signal is more than 10 dB， the least squares method is applied to estimate the amplitude of various inter-harmonics without de-noising. The harmonic analysis of numerical simulation signal， amplitude modulation signal and electric arc furnace current shows that the method has strong anti-noise ability， fast calculation speed and high-accuracy. This method especially has strong adaptability to the amplitude modulation and time varying inter-harmonic signal. Simulation results show the feasibility and effectiveness of the method.