Abstract: Desertification is one of the most serious environmental problems in the world and one of the global major problems established by the United Nations. And the matter of desertification pattern is one of the most important aspects in the study of desertification, because it has close relation to the understanding of the essence of desertification and the prevention of desertification. First of all, a new definition of the concept "desertification" is given in the paper. Then three questions are discussed or analysed. First, the situation of the desertification in Sahel is introduced, and a popular viewpoint about the desertification pattern is mentioned and discussed. According to the viewpoint it seems that the desertification is the result of advancing or creeping southwards of the Sahara north of Sahel. It is not correct and doesn't tally with the actual situation. Second, four mechanisms of the desertification in Sahel are put forward, and they are overgrazing, overcultivation, firing and overgathering of firewood. Third, based on the analysis of the four mechanisms mentioned above it is pointed out that the desertification is produced from the Sahel zone itself, basically not from the outside. Obviously, the results of the processes or mechanisms of desertification are the same, that is the formations of deserfication land patches. Ususally serious overgrazing will produce bare land patches in different sizes because it often take place around wells or other water source points and some pasturelands with good grass. Unsuitable cultivation always happens in some places with rich soil and moisture, leading to the formation of bare desertification land patches. Other desertification mechanisms have the same results. With the passage of time these desertification land patches in Sahel gradually increase and enlarge, finally merge together, and join the Sahara, and it looks as if the Sahara advanced southward. In fact the Sahara doesn't move on. Someone with that viewpoint considers that a greenbelt (shelter forests) should be built along the edge of the north part of Sahel to prevent desertification in it. As mentiond above the desertification take place in the zone itself, the greenbelt measure will not reach the goal.

Key words: geography, integrated research, land system science