Reflecting on the last law approved regarding the criminal procedure of Iran, proves the sovereignty of the principle of unity of judges over the proceedings of the judicial system, despite the relative sovereignty of the mixed judicial system. The principle of the unity of the judge allows the prosecutor as the prosecuting authority to enter the field of investigation and investigation, contrary to the principles of the mixed system common in Anglo-Saxon countries such as America, England, Germany and Italy, and on the other hand, France. The distinguishing feature of the common mixed system in the preliminary investigation phase of Iran with the Anglo-Saxon and French countries is the involvement of the prosecutor in the investigation and investigation, in such a way that the prosecutor in the mentioned countries is only responsible for the prosecution and ultimately the investigation, and there is no interference in the investigation. And according to the issuance of judicial orders, this is despite the fact that according to Article 92 of the Criminal Procedure Law of Iran, the prosecutor as the prosecuting authority can simultaneously be responsible for the prosecution, investigation and judgment. In fact, the the proceedings from each other in order to observe the, unlike other countries in the field of legislation. Therefore, it is desirable that the prosecuting authority, based on the principle of separation of powers, cannot rely on the seat of the judicial office, and at the same time have the three roles of prosecuting, investigating and judicially.