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Inverse synthetic aperture radar (ISAR) imaging of non-uniformly rotating target is very significant in many applications. In this case, the Doppler frequency for a scatterer is time-varying, and the traditional Range-Doppler (RD) algorithm is not appropriate for the azimuth focusing. In this paper, the received signal in a range bin is assumed to be multi-component polynomial phase signal (PPS), and a novel approach for ISAR imaging of non-uniformly rotating target via Range-Instantaneous-Doppler-Derivatives (RIDD) algorithm is proposed. For the RIDD algorithm, the cross-range resolution is derived by the arbitrary order of Doppler derivatives, and it is the generalization and extension form of the traditional Range-Instantaneous-Doppler (RID) and Range-Instantaneous-Chirp-Rate (RIC) algorithms. Results of simulated and raw data demonstrate the effectiveness of the new method proposed.