This paper focuses on the changes of the basic nonbasic economic activities in Guangzhou since the middle of 1980s. The attention is initially paid to the composition and change of urban basic nonbasic economic activities. Four research findings have been achieved. ① The general change tendency was that the scale of urban basic economic activities was smaller than that of nonbasic ones and showed the tendency of becoming smaller with time. The secondary sector showed the shrinking scale of basic activities but the tertiary sector had a reverse change. ② The scale of the basic economic activities of industry shrank and experienced a shift of the basic part being bigger than nonbasic part towards smaller than nonbasic, but industry was still the major economic basis of Guangzhou. ③ The proportions of basic and nonbasic parts of many tertiary trades changed, i.e. as the former rose, the latter fell, or the basic part had a relatively high proportion all the time, which strenghthened the status of the basic activities in urban economic development. ④ The fact, the basic employment (basic population) of producer services increased with a faster speed than the total employment and accounted for nearly 10% in the total employment, indicated that the producer services were becoming one of the important components in the urban economic basis and had the huge potential and possibility of occupying the regional market. Then the analysis was turned to the external function of the producer services based on questionnaires. The results showed that: ① In the producer services of Guangzhou, there indeed existed basic economic activities of exporting services to its surrounding regions (Guangdong Province, the whole country and the overseas). ② The differences of the external functions among the trades of producer services were obvious. The finance and insurance sectors had smaller proportions of providing services for the areas outside of the city than other sectors like information consultant, computer application, and scientific research and technological services. ③ The producer services in Guangzhou serviced mainly for Guangdong Province, which showed that the development level and scale of producer services were limited and their international market was narrow. Thirdly, the economic base theory of urban development was discussed. The research results showed that services not only provided services for cities themselves but also export services to the areas outside cities. And producer services mainly provided services for the areas outside cities (i.e. mainly being basic economic activities) which indicated that producer services have the function of engineering economic growth. The substance of development of basic economic activities lies in the tradability of services. Several factors, information technology, transnational enterprises of services and transformation of government function, have resulted in the services’ tradability. All these changes made the relationship between basic economic activities and urban development more complicated than before. A re explanation to the traditional economic base theory, paying more attention to interaction between urban economic activities and the location significance of the theory, was made. With the technological progress, the impacts of basic economic activities on urban development by stages have been identified. All these imply that the classic theories have not well explained the urban development in the post industrial society and it is very necessary to make the re explanation to the classic theories and build new theories.