The converters in DC transmission project can produce the large number of harmonics which may have harmful effect on the power system stability and the communication lines. In order to effectively reduce the converter harmonics hazards and improve the system reliability, this paper analyzed the time-frequency domain characteristics of converter harmonics in ± 800 kV UHV DC transmission project. According to the relationship between the converter harmonic current，the system operating power and the DC current value in transmission project, the harmonic current distortion rate was presented as the eigenvalues of current harmonic characteristics. Based on the operation characteristics of transmission project, the change law of harmonic current with the increase of transmission power and DC current could be effectively characterized by the harmonic current distortion rate. The study results can provide the theoretical basis for the analysis on converter harmonic characteristics in DC converter stations, as well as the theoretical guidance for the harmonic treatment in subsequent projects and the filter design optimization.