According to the Criminal Procedure Code, the legality principle governs the authority of public prosecutors. However, they still have board discretion. Not only the Criminal Procedure Code provides that, but also the statistic shows so. Therefore, what constitutional principle public prosecutors should comply with is essential. In the United States, the equality protection clause prohibits discriminatory prosecution while the due process of law forbids vindictive prosecution. Our Constitution also has the requirement of equal protection and due process of law, which should govern public prosecutors. The legal framework, provisions, and precedents could be those lessons for the revisions of the Criminal Procedure Code.