Abstract: It is important to characterize the change of soil environment and its affecting factors in oasis for protecting oasis stability and achieving rational development in the process of oasification. In this study, the Qira Oasis was selected as the study area to analyze the change of soil particle size distribution (PSD, an important soil physical property) and its affecting factors at different depths based on the fact that farmland was the main land use type in the oasis. Fractal theory was used to describe PSD based on the PSD data at depths of 0-20 cm, 20-40 cm, 40-60 cm and 80-100 cm in sample plots in the oasis. According to the comparing and clustering analysis of PSD fractal dimension, the study result revealed that there was a significant difference of PSD among the sample plots at each depth, and the differences of farmland use years and locations were the main reasons resulting in the difference of soil PSD. At the depth of 60 cm, the dominant factor resulting in the difference of soil PSD was the farmland use years, especially at depth of 0-20 cm. However, its effect was gradually decreased with the increase of depth, and even there was no any important effect at depth of 80-100 cm. Therefore, there is a positive effect for PSD and soil environment to protect farmland which ensure the sustainable cultivation of farmland in the process of oasification.

Key words: oasis, farmland, soil particle size distribution, fractal theory, Qira