Lying in the hinterland of the Taklimakan Desert, the Keliya River forms a mystic green corridor. Revealing the distribution features of the lower reaches of this fossil river is of great significance in the ecological construction and the groundwater source survey. Using X-band airborne SLA image as an important information source, combined with field investigation, this paper studied and analyzed the fundamental principle of this technique and the airborne SLA imagery features, stretching characteristics and changing process of the river course. By sampling data and sampling mathematical model, the authors approached the penetration effect of the airborne SLA image. The study indicates that the X-band of the airborne SLA image can penetrate a depth of 14.6cm in the region of background desert, and 10.34cm in the fossil river bed.