The invention discloses a power-transmission-line atmospheric-environment corrosion-severity rapid assessment method. The method comprises the following steps of through an atmospheric corrosion monitor, detecting a maximum stable corrosion current of an assessed power-transmission-line atmospheric environment, and according to the maximum stable corrosion current and a preset atmosphere environment corrosion severity grade-pollutant equivalent current relation table, determining a first corrosion severity grade of the assessed power-transmission-line atmospheric environment; through the atmospheric corrosion monitor, detecting a corrosion electricity quantity of the assessed power-transmission-line atmospheric environment, and according to the corrosion electricity quantity and a preset atmosphere environment corrosion severity grade-corrosion electricity quantity relation table, determining a second corrosion severity grade of the assessed power-transmission-line atmospheric environment; selecting a result with a high grade as a final evaluation result from the first corrosion severity grade and the second corrosion severity grade and outputting. By using the method in the invention, a basis can be provided for construction, material selection and anticorrosion maintenance of a power transmission line and advantages that reliability is high, accuracy is good, the method is simple and easy to use, and detection time is short are possessed.