It is very challenging and may not conform to legal facts and ethical standards for a defendant who has been sued for illegal arms trading to rationalize his behavior in support of the right to self-defense, because illegal arms trading itself is an illegal act and cannot be justified. However, from the perspective of hypotheses, it may be possible to discuss the following ideas: first of all, we must collect evidence that the defendant's environment seriously threatens his life and safety, such as a series of violent intimidation incidents against the defendant, frequent violent conflicts in the defendant's life or workplace, etc., to prove that the defendant is in a state of extreme fear for his own safety.In a situation of serious violations. At the same time, investigate in detail the specific circumstances of the defendant's acquisition of weapons to see if there is a situation where the law and order in the area is chaotic, it is difficult for legal means to effectively guarantee one's own safety, and one has to obtain weapons by extraordinary means to enhance one's own defense capabilities. And to show that the defendant did not actively provoke or commit any behavior beyond the scope of reasonable self-defense after obtaining the weapon, but only to be able to protect himself in the face of imminent danger. However, it must be emphasized that in actual legal practice, illegal arms trading is difficult to be justified as an act of self-defense. The law has a clear purpose and regulations for the control of weapons, aimed at maintaining public safety and social order. Any defense that attempts to rationalize illegal behavior needs to be strictly based on facts and legal provisions, and the probability of success is usually low.