Abstract: To explain the moral issues by using the psychological mechanism "sympathy" is a unique symbol of Hume's moral philosophy.In fact, "sympathy" is a principle that reproduces some emotion of others through the imagination.Hume made "sympathy" become a basis of a universal moral judgment through amending subjective "sympathy",and he had seen it as a tendency to all members of society rather than an explanation of individual's emotional exchange.People go beyond the heart of self-respect with sympathy and mutual understanding,thus the morality and virtues of "mercy" and "justice" were able to be formed.The support of the emotional mechanism is still needed in the revival of the contemporary virtue ethics,so the principle of "sympathy" plays an essential role in the formation of virtues and the establishment of the moral rules and generalization.