Population aging is an irreversible changing tendency of urban population age structure at present and for a long time in the future, and this tendency inevitably has significant and continuous influence on urban economy in future. Therefore, it is necessary and important to make clear the action mechanism and the influential effect of population aging for urban economic growth. On the basis of previous researches as well as intermediate and microcosmic data, Shanghai is taken as an example in the article to discuss and analyze the influence of population aging on urban economic growth by virtue of Solow growth model from the new view angle of closed city and open city. Meanwhile, the article focuses on disclosing the aging dilution effect generated by the labour mobility under open city system, the restraint effect on the negative influence generated by continuous high R&D investment to population aging, etc.