The invention discloses a direct-current transmission conductor dirt evaluation method and system. Particulate matter will attract charged ions to become new charged corpuscles, and consequently an ion flow field of a direct-current transmission conductor becomes more complicated. The evaluation method comprises the steps that a to-be-evaluated conductor is selected, and air pollution indexes in atransmission conductor area and rainfall meteorological data in a corresponding time period in a to-be-evaluated conductor area are collected; for a whole dirt accumulation process, an accumulation-cleaning model is adopted to calculate the accumulation condition of pollution particles around the conductor on the conductor; the accumulation condition obtained through calculation is substituted into the accumulation-cleaning model, and a conductor dirt cleaning condition in the corresponding time period is obtained and converted into equivalent salt deposit density; and the equivalent salt deposit density is compared with standard salt deposit density, and the dirty level of the current direct-current transmission conductor is judged. According to the direct-current transmission conductordirt evaluation method and system, the changing condition of the ion flow field on the surface of the conductor is calculated through the air pollution indexes and the meteorological data and then converted into the changing condition of equivalent salt deposit density, and therefore the dirty condition of the conductor is judged.