In this article, first, the texts of the reports related with the formation of Osama army are investigated, and then the motive of army formation, the reason for the Prophet’s emphasis on moving the army and the reason for its lack of movement have been explored. This exploration clarifies one of the most exact governmental policies of the Prophet of Allah (s) and as the analysis of the aforementioned reasons has been based on the stated events of his life’s last months and also investigating the calendar of the army formation, so due to this two reasons it its explored here briefly.