The firstinstance judgment of “Yu Huan case” triggered a great discussion on the criteria of the identification of legitimate defense in the academic and practical circles. It has become a landmark case in the academic circle to reflect on the legal issues of judicial application, and was selected in the 18th batch of guiding cases of the Supreme Court. The judge of German Berlin wall guard case always follows the justice concept of law, which shows the warmth and value of law. In the first trial of “Yu Huan case”, the lack of the investigation of the life experience and legal application of the conviction and sentencing of the case failed to correctly identify the legitimate defense, resulting in the sentencing deformity, which affected the impartiality and rationality of the referee. In order to avoid the recurrence of similar behaviors, focusing on the change from ethics to jurisprudence of the judges' thought, paralleling fair trial and judicial openness, and precluding interference with fair justice, the referee can uphold the spirit of advocating the law and judge according to law.