The aim of this article the reality of the informal sector in the Algerian city, and try to do a diagnosis of this important geographical and economic issue, has been chosen the category of informal trade in the city of Souk Ahras, and this is in order to highlight all aspects of this trade through its manifestations, circumstances, motives, causes, and the extent of its impact on the city s urban and economic, environment, especially as it has become a prominent manifestation of urban life and one of the Algerian factories that control the growth and construction of the city, and the source of this important in the creation of employment and informal wealth in the city, from our study of the reality of this informal sector at the level of the city Souk Ahras, we found that it is endemic mostly in the sector of the centre of the city as represents the most strong hierarchical level in the city in terms of radiation and vital attraction, as urban unemployment that characterizes the category of the official labor force is among the most prominent motives that led to the demand for this trade irregular.