It may happen that due to the conflict between the citizenship laws of the countries, a person has dual citizenship. In order to distinguish practical or effective citizenship, pieces of evidences and circumstances should be considered and it should be considered which government a person belongs to and is more dependent on in practice. In this sense, the place of residence, the citizenship of the person's spouse and even the passport that has been used, and finally the choice of the person himself, which is also very decisive, are taken into consideration. Slow the importance of citizenship comes from the fact that since an individual does not have an unquestionable position in international law, the government is a means of providing this position for him, so the support that the government can give to an individual depends on the works and role of the individual citizenship relationship. This research with a descriptive-analytical method states that in Iranian laws, the original citizenship through the blood system and paternal relationship and the Jus Soli system has been accepted with completely exceptional conditions and in a partial way, and while it has given more priority to the blood principle, In English law, which is subject to the common law legal system, it has accepted the system of land and residence and modified it with the principle of blood.