Legitimate defense plays an important role in curbing crimes,maintaining public order and fostering good moral conduct.In China’s judicial practice,cases on legitimate defense raised several controversies on the nature of legitimate defense,limits of excessive defense and the applicable objects and definition of special defense.The nature of legitimate defense mainly involves defense intention,defense object,defense time and other factors.The defense intention is an important sign to differ the legitimate defense from the illegitimate defense.The object of legitimate defense can only be the unlawful infringer and the actor can only prevent the ongoing illegal infringement.The existence of unlawful infringement of reality is a prerequisite for legitimate defense to be exercised.The unlawful infringement that is justified by defense should be illegal,invasive,urgency and realistic.As an unlawful infringement,the excessive defense needs to be distinguished from the legitimate defense in terms of the defense limit.As for the “necessary limit”,in principle,it means the necessary defense can stop the present unlawful infringement,and there is an obvious difference between the illegitimate defense and legitimate defense in terms of the means of the actor and the intensity of behavior.Defense behavior shall be treated as excessive defense only if it “obviously exceeds necessary limit” and “cause great harm” at the same time.The key to apply the special defense lies in the accurate understanding of the applicable object of special defense,that is,special defense can only be applied to “ongoing physical assault,murder,robbery,rape,kidnap and other violent crimes that seriously endanger personal safety”.