High altitude electromagnetic pulse (HEMP) may cause failure or damage to wide-area infrastructure. For economic reasons, it is necessary to evaluate the vulnerability of key electrical and electronic equipment under HEMP This study combines uncertainty quantification with equipment effect assessment. Based on the idea of margins and uncertainties quantification (QMU), this paper summarizes the procedures of vulnerability assessment method for electrical and electronic equipment based on QMU. First, select the key parameters of the equipment, usually the norm of coupling channel current and voltage; Second, obtain the probability distribution of key parameters under HEMP as the stress of equipment by numerical simulation and uncertainty quantification; Then, carry out the HEMP effect test and estimate the probability distribution of equipment effect threshold as the strength of the equipment; Finally, by calculating the Euclidean distance between stress and strength of the equipment, calculate the QMU metric and evaluate the equipment vulnerability by the QMU method. This study uses an example to illustrate the feasibility and procedure of the vulnerability assessment method based on QMU.