The chief reason for why resources economics haven't come to be a mature subject is that scholars haven't reached a common opinion of their research object.There are mainly two problems:The first is no demarcation line has been drawn between resources economics,envir-onmental economics and ecological economics in terms of extension and intension of research ob- ject.The second is to turn resources economics into reasonable collocation of natural resources or utilization economics.According to the relations of population,natural resources,environmental resources,natural disasters and eco-systems,and the seven cross systems that they form separately with economics,this paper differentiates the research object of resources economics and six correlative economics.According to the special contradiction of scientific research object,this paper marks off resources economics,environmental economics and ecological economics.Again according to the general definition of economic activities being the research object of economics,the research objects of three kinds of economics are generally confined seperately.Also,resources economic activities are regarded as the unification of the essence,course and development of resources economy.