Abstract: Land desertification is a serious global environment problem.Many studies on the causes and evolution of land desertification have been undertaken by specilists and schoolors,and the main causes are natural and anthropogenic factors.In this paper,the Gonghe Basin,Qinghai Province is concerned.The Principal Components Analysis of influential factors,such as population for farming and animal husbandry,livestock numbers,cultivated area,precipitaion and moderate gale days in 42 years,proved that the first principal components,the most major synthetic indexes,are the absolute values of population for farming and animal husbandry,livestock numbers and cultivated area,their offer rate is 46.5 percent;the second principal components are precipitation and moderate gale days,their offer rate is 24.6 percent;the third principal components include not only natural factor but also man made factor,their offer rate is 14.9 percent.The results indicate that the population growth has strengthened the pressure on the environmental system,and because of the unreasonable economical actions,such as cutting firewood and uprooting medicinal materials,and so on,the desertification degree has been deepend and the area has been increased,therefore,the main reason of desertification is caused by population pressure.

Key words: land desertification, influencing factor, quantitative analysis, Gonghe Basin