Through the analysis of the factors influencing the development of regional economic geography as well as the evaluation of the present situation of reional economic geography, the authors of the paper probe into the research object, the fundamental theories, the main sub theories, as well as the theoretical structure of regional economic geography in China in the 21st century. The paper suggests that (1) the theories of territorial division of labor and motion of economic regions are regarded as the fundamental theories of the subject; (2) the conditions and the elements of the economic regions should be both inter-related and distinguished with each other; (3) the study of the structure (i.e, the industrial structure and the spatial structure) and the function of the economic regions, as well as the analysis and evaluation of the economic regional types, should be emphasized; (4) the geo economic regional system should be added to the already existed economic regional systems. In addition, the paper puts forward several principles on the theoretical construction of the subject, in which the relationship of the inter infiltration, inter-competition and the independent development of regional economic geography and other neighboring subjects, especially regional economic geography and regional economics, is stressed on. As a result, the paper advances countermeasures for the construction of the theoretical system of regional economic geography.