Abstract: Arable land resources are not only the basis of human survival,but also the most important type of land use.In recent years,with the development of urbanization and industrialization,the phenomenon of alienation of arable land for construction has become more and more serious.Therefore,based on the functions（social security,ecological service and economic production） of the arable land resources,a value assessment system for arable lands was tentatively established.The system used comprehensively the market valuation method,substitution method,opportunity cost method and shadow pricing method to assess losses in the value of positive effects of the land resources after being converted from arable land into construction land in 12 cities of Gansu Province.Results show that the loss was great.A total of 1 564.66 hm2 of farmlands were converted into construction land in 2007,bringing about a loss in value of the land reaching 95 904.09×104 yuan or over 45×104 yuan per hm2 in all the 12 cities.From the structure of total value loss,the loss in direct use value was 45 712.77×104 yuan and in indirect use value 50 191.32×104 yuan.It is quite obvious that besides its value in providing produce directly to the society,the arable land resources have enormous indirect use values,which are more significant than the former in contribution to mankind.

Key words: social value, ecosystem service value, economic output value, arable land resource, Gansu Province