Abstract: 【Objective and Method】This research taking the alluvial-fan oasis in Manas river as an example, through the fixed position experiments, the trend estimation model of principal component analysis and so on, the succession of plants and soil characteristics of field in the bottom of alluvial-fan oases were investigated and analyzed．【Result】With the increase of years of reclamation the salt-loving, perennial plants were substituted by annual plants and then entered a stable stage after 6-8 years. Total salt content decreased gradually and then increased, which reached the lowest after reclamation for 9.46 years. The soil nutrient showed the contrary to sail. The comprehensive quality of soil was a positive development in the first 10 years and then turned to degeneration. Through the trend estimation model of principal components analysis, farmland attains to the best performance in quality till 10 years. 【Conclusion】Synthetically analysis the various index of the soil quantity, so 10-15 years could be used as early-warming time to reflect the change of soil quality.

Key words: Oasis farmland, Years of reclamation, Soil quality, Early-warming