The index of eqipment and system in the electromagnetic compatibility standards is uaually suitable to many kinds of flats, and it is to be right chosen and clip in the actual application based on the engineering practice, or excess design and absent design will bring waste of resouce or electromagnrtic interference. To the naval ships, it is difficult to carry throngh accurate modeling adopting traditional numerical simulation method. Recur to probability statistial analysis, we research the rule of electromagnetic emission of pontential interferential equipment and sensitive characterisitic of pontential sensitve equipment, by whic forecast the probability of resulting in electromagnetic interference and farther to process analysis and decision-making of equipment and system index. This meth on the one hand fully makes use of engineering historical data which have preferable engineering value and directive sense, while on the other hand it avoids abundant numerical modeling which is more simple and feasible