Abstract: The deposition process of the loess in Ili valley in Xinjiang is controlled by circulation of Atlantic Ocean west wind, which is different from the deposition process of East Asia monsoon-controlled loess in Loess Plateau. Based on the in-situ comprehensive soaking tests on a channel project, it is been proved that Ili loess is a kind of strong collapsible loess. Furthermore, the collapsibility is characterized by early development, fast speed and large value. According to the field measurement, the maximum self-weight settlement reaches a large value of 352 cm, and the maximum collapsibility coefficient is 0.18 (p=200 kPa). From the history of sediment, the formation age of Ili loess is young. The deposition process is drier and cooler, and it is not influenced by hot and humid climate. Thus, there is less effect of rainfall-leaching on salinity, especially on calcium carbonate. In consideration of its physical property and mineral composition, the natural density, moisture content and saturation of Ili loess are low, while the dissolved salt content is high. The micro-structure observations indicate that the Ili loess has the characteristics of point contact, aerial structure form and few cementations, which lead to a highly unstable structure and strong potential collapsibility. These are historic and internal factors that cause strong collapsibility.