Abstract: In recent years, among various power quality problems, voltage sag has become a major factor affecting the normal and safe operation of power-using equipment, resulting in huge economic losses. Therefore, the voltage sag has been widely concerned by the power supply department, power-consuming enterprises, power equipment manufacturers and other parties. Based on the complexity of grid topology and the randomness of voltage sag events, Monte Carlo simulation method is used to obtain the voltage sag information of a point-of-common coupling (PCC). According to the influence mechanism of voltage sag on the sensitive process, the probability of sensitive process interruption caused by voltage sag is obtained. Based on Mahalanobis distance, this paper creatively proposed a method to evaluate the probability of sensitive equipment trip, which considers the severity of the voltage sag duration and the severity of the sag amplitude，lays the foundation for accurately evaluating the probability of sensitive process interruption. This paper analyzes the negative impact caused by voltage sag on enterprises and society, comprehensively considering the direct and indirect economic losses of voltage sag， accurately evaluating the economic losses of voltage sag. Finally, an economic losses assessment of a voltage sag in a chip manufacturing enterprise in Southwest China shows that the evaluation method in the paper has a clear process flow and good operability.