Abstract: Detuning of DC filter in ultra high voltage direct current(UHVDC) transmission system will increase the harmonic content, and the location of the detuning component has important application value for improving the operation reliability of DC filter. A method for detecting detuned components in a dual tuned DC filter based on fault recording is proposed. Firstly, the components are grouped according to the filter structure, and the electrical quantities of the recording points recorded by the system after the fault are used to calculate the amplitude of harmonic current and harmonic voltage using Fourier decomposition. After theoretical deduction, a specific number of harmonic current ratios and harmonic impedance are selected as characteristic variables, by implementing a one-to-one correspondence between the direction of component parameter changes and the direction of feature quantity changes, the detuned components in each group can be identified, and under the assumption that at most one component in each branch is detuned, the sum detuning degree of the detuned components can be further calculated. Finally, the correctness and validity of the proposed method and criterion are verified by the calculation and analysis of PSCAD simulation data and on-site recording data, providing a practical method for locating the detuned components of DC filters.