The main issue tried to be investigated in this article is what is the structure and process of the preliminary branch of the International Criminal Court? This article is descriptive and analytical and the mentioned question has been investigated using the library method. The findings indicate that the existential philosophy of the establishment of the preliminary branch, in the face of the prosecutor's office, is that countries at the time of the Rome Statute, wanted to establish an institution that could protect the prosecutor from any suspicion of non-compliance with the standards of justice and fairness. Therefore, with the establishment of the preliminary branch, the way is closed to any doubt in the performance of the duties of the prosecutor. The preliminary branch of the International Criminal Court is an advanced judicial system that has been able to meet the goals of a standard trial to some extent by the interaction of the prosecutor's office in the preliminary investigation phase, by issuing the necessary licenses and regulatory policies. The result is that at the stage of starting the prosecution and conducting the preliminary investigation, if the prosecutor does not want to observe the principles of justice and fairness as an impartial judge, he can easily start the prosecution against a country and this is the preliminary branch that prevents this.