Aiming at the problem that unsteady harmonic parameters are difficult to be accurately detected, this paper improves variational mode decomposition by means of the energy contribution rate of modal components, extractes modal components by adaptive decomposition of harmonic signals, and constructes a new K-M mutual convolution window using Kaiser window and maximum side-lobe decay window. The correction formula of bispectral line unsteady harmonic parameters based on K-M mutual convolution window is derived, and the detection method of unsteady harmonic parameters based on adaptive variational modal decomposition （VMD） and a new K-M mutual convolution window is proposed, and the experimental platform of unsteady harmonic parameters analysis based on digital signal processer （DSP）is developed. Simulation analysis and actual measurement results show that the proposed method can effectively and accurately detect the unsteady harmonic parameters under the interference of noise and fundamental frequency fluctuation. Compared with the traditional harmonic analysis method, the proposed method is suitable for unsteady harmonic analysis and has high precision of harmonic detection.