Abstract: Studies show that arid area oasis cities and towns are in closure situation，and urban development is relatively slow，so，the external factors play an important role in the agglomeration progress. Fixed assets investment as an intervention factor of higher levels of government for local development is an important thrust to urban development in the arid area. This paper is intended to study the features of fixed asset investment in the Economic Zone on the Northern Slope of Tianshan Mountains from 2000 to 2009，including three indicators: investment concentration coefficient，the investment [H] index and the government-led degree. Then, collecting socio-economic data in this region，and using the entropy method the urban agglomeration index was calculated of all towns from 2000 to 2009. On this basis，using the principal component analysis and panel data model, the influence was quantitatively analyzed of fixed asset investment and mechanism to urban agglomeration. The results show as follows: （1） the distribution of fixed asset investment in the Economic Belt on the Northern Slope of Tianshan Mountains concentrated in regional central cities is obviously "ordinal-scale" distribution and has the characteristics of administrative region economy. The government leading degree and investment concentration degree have a reverse relationship. （2）The urban agglomeration in the Economic Belt on the Northern Slope of Tianshan Mountains is mainly the process of economic concentration and land conversion process at the first, the concentration of the urban population process in the second place, and the last is the increasing of the social life level. （3）Administrative force, as a representative of fixed asset investment, is one important driving force of urban agglomeration in the Economic Belt on the Northern Slope of Tianshan Mountains. This driving force has a stronger role in the higher administrative level areas and the higher industrialization level areas. （4）The effects of fixed asset investment to urban agglomeration in the Economic Belt on the Northern Slope of Tianshan Mountains are different in the different periods. In the initial stage, the investment mainly promoted the increasing of the urban scales; in later stage, the investments promoted not only the increasing of the urban scales, but also the urban economic concentration.

Key words: investment in fixed asset, the government leading degree, urban agglomeration, mechanism, the Economic Belt on the Northern Slope of Tianshan Mountains