The principle of equity is one of the important issues in jurisprudence and law, and its various aspects have always been the subject of debate. The present paper is descriptive-analytical, and the mentioned question is investigated using the Library research method. The findings of the paper indicate that equity is widely used in jurisprudence in the form of the principle of justice, and the principle of equity can be inferred in jurisprudence rules such as La-Zarar and Principle of Equality. In criminal law, the principle of equity is not used as a legal principle. Nevertheless, it has contributed in fair proceedings and has been at the center of the attention of the legislature in issuing decisions in cases such as reductions in discretionary crimes. The Principle of Equity has not been reflected in criminal law to its fullest potential, therefore, it is necessary to present it as an effective rule so that jurists and judges can evaluate the regulations of criminal law by such rule, and put aside whatever they find contrary to justice and equity, in an attempt to issue a decision which is appropriate for justice and equity.