Abstract: Based on the material composition, the geochemical nature, palynoflora study and age dating it is assumed safely that the loess is aeolian deposit mostly originating from the deserts in Tarim Basin under fairly dry climate of steppe type, and overspreaded piled mainly from the last glaciation maximum through Holocene period, which might be related to the time when the Taklimakan deserts were extensively formed. The occurrence of the frequent modern wind-blown dust precipitation along the south margin of Tarim appears to be the modern loess accumulation, meaning that the loess kept depositing strongly since the last glaciation maximum. The palynofloras indicate that the biological environment associated with the loess deposition is quite similar with the modern one at the northern slope of Kunlun Mts. It is supposed that the modern lower general circulation, related to the loess formation, was completely set up probably in the last glaciation maximum. On the arid background occurred some moist fluctuations. Around 7000 to 5000 a. B. P. was a prominent humid oscillation when thick soil developed and snail, Succinea pfeiferi, with semihumid habitat, thrived. It might be 50 to 100 mm more in annual rainfall than what it is today.