Abstract: Sliding discrete Fourier transform (sliding DFT) algorithm has disadvantage on instability of outputs, which is influenced by the finite register length effects of digital system. Frequency units of sliding DFT are reconstructed by using recursive units of improved Goertzel algorithm, which can provide initial spectrum value and a new accurate spectrum value every N points. Improved sliding DFT algorithm can process data continuously and can keep output stabilization for a long time, which becomes increasingly important at real-time consecutive time-frequency spectrum analysis.