Abstract: Barchan's retrograde evolution was that the volume of a barchan was be coming smaller gradually and vanished finally. Field observations were made in complex ridge area near Tazhong 4 well in Taklimakan Desert. During the period o f observation, the volume of dune was decreasing and some barchans disappeared. The height, the number, the sand amount and the density of barchans reduced from the foot of complex ridge's lee side to the middle of interdune corridor of complex ridges. There were no dunes about 300 m from the foot of complex ridge's lee side, which showed that barchans disappeared after having moved for 300 m at least. The slope of barchan top was small and some barchans occurred the crest/brink separation, which showed that the amount of erosion was more than that of accumulation. All of these proved that barchan's retrograde evolution occurred in the studied area. The amount of deposition was decided by dune form, wind velocity and saturation degree of wind sand flow. The amount of erosion was decided by sand loss a t the horns and sand loss detained on the sand sheet. When erosion was more than deposition, barchans occurred retrograde evolution. The barchans which occurred retrograde evolution were located near the lee side of complex ridges. The win d speed was accelerated in this area, which combined by flowing over coarse sand covering sheet resulted in the formation of unsaturated shifting sand flow. The erosion function of unsaturated flow was the dynamic factor of barchan's retrograde evolution. If the speed of barchan's retrograde evolution was measured by the rate of dune's volume variation, t he speed of retrograde evolution falled dowm exponentially with the increase of dune's height according to the field observations. The barchans higher than 3 m did not occure retrograde evolution in the wind environment of the studied are a. When barchans were about 2 m high, they couldn't keep erosion deposition ba lance, which is the internal factor of retrograde evolution. In addition, secondary wind decreased the width of barchan, which reduced deposition. The coarse s ands moved to the base of barchan in stronger wind and they could not be moved b y the weaker wind. When barchan moved, these sands were detained, which accelerated the barchan's retrograde evolution.

Key words: Taklimakan desert, Interdune corridor, Barchan, Retrograde evolution, Dune form