Deductive reasoning is a common reasoning method in the application of criminal law,which consists of three parts:major premise,minor premise and conclusion.Since Beccaria proposed the judicial syllogism,the syllogism on the application of criminal law has become a basic logical method for describing the activity of the application of criminal law.In the application of the criminal law under the principle of legality of crimes,the conviction process shall be completed in strict accordance with the method of deductive reasoning,to form a credible conclusion on convic-tion.In the deductive reasoning of criminal law,the legal rules determined by the major premise should be limited to the express provisions of the criminal law,and on the basis of ascertaining the facts of the case,the legal nature of the act should be finally determined through the legal subsump-tion.