It is easy to embrace equalitarianism intuitively, but it is quite difficult to justify the theory of equality. How could Equality be justified? Contemporary equalitarian proposes four basic justifications: the justification based on dignity relies on a metaphysics of human nature, which deduces the equality of a person from the dignity of human beings; the justification based on procedure maintains that inequality needs reasons, while equality does not need reasons; for the justification based on fairness, equality depends on fairness that depends on some theoretical hypothesis(the original position or the motive of impartiality). Compared with the aforementioned justifications, the contractualist justification is more reasonable, which appeals to the consent of all persons for equality. However, each of the four justifications has some difficulties that are hard to overcome.