Voltage sag is one of the serious power quality issues in industrial parks. In order to make a reasonable and accurate assessment of the severity of voltage sag events in industrial parks, a voltage sag assessment method for industrial parks based on the tolerance of sensitive equipment was proposed. Firstly, considering the evaluation deficiencies of the severity index for voltage sag S_e, S_e of was improved and the improved voltage sag severity index S_en was proposed. Based on the given equipment sag tolerance factor G_i based on the tolerance curve and the sag type influence factor y_n based on the equipment power phase, the voltage sag severity indicators for different sensitive equipment Q_i was proposed, and a comprehensive index of voltage sag severity for industrial parks K was proposed by combining the above indicators. The example verifies that S_en can overcome the evaluation defect of traditional S_e index, and the indices Q_i and K can reasonably evaluate the severity of voltage sag in industrial parks.