The utility model relates to an automatic insulator salt deposit density online detection device which comprises sampled insulators, a cleaning arm mechanism, an opening-closing type sealing cover and a salt deposit density measurement instrument, wherein the cleaning arm mechanism, the opening-closing type sealing cover and the salt deposit density measurement instrument are arranged inside a device box. The sampled insulators are hung on an electric device, and due to the fact that the working condition of the sampled insulators is the same as that of operating insulators, the dirty state of the insulators can be represented through that of the sampled insulators; when the automatic insulator salt deposit density online detection device is not used, the sampled insulators are hung outside the device box of the automatic insulator salt deposit density online detection device, and the cleaning arm mechanism is sealed in the opening-closing type sealing cover; when measurement is required, the sampled insulators are lifted into the device box, the cleaning arm mechanism is moved out of the opening-closing type sealing cover to automatically clean the sampled insulators, a cleaning dirty solution is collected, and the salt deposit density numerical value can be measured through the salt deposit density measurement instrument. The automatic insulator salt deposit density online detection device is convenient to use, high in automation degree and suitable for all-weather automatic measurement on the salt deposit density of the insulators, the dirt accumulation state of the insulators can be accurately reflected, and data supports are provided for safe operation of a power grid.