Dense frequency signal refers to the signal containing harmonic and interharmonic components that are very close to each other in frequency domain. Due to the limited frequency resolution and the existence of spectrum leakage and fence effects, it is difficult to accurately detect the harmonic and interharmonic components in dense frequency signals. The spectral interference under asynchronous sampling conditions can lead to the failure of measuring the multiple adjacent harmonics and interharmonics. Therefore, this article proposes a mixed dense signal harmonic and interharmonic analysis method. The dense frequency signal model is first established. Based on the model, the discrete Fourier transform results of the dense frequency signal are processed by local mean decomposition extension to construct that single multichannel signal as a virtual multichannel. Then, the parameters of each frequency component are obtained by means of principal component analysis and fast independent component analysis. Finally, the measurement of dense harmonic and interharmonic components is implemented. The simulation and experimental results show the high accuracy and the noise resistance ability of the proposed method in identifying and measuring the dense harmonic and interharmonic components.