The population situation enters into a period of low birth rate,low death rate and low natural growth rate since Chongqing became a municipality,the dependency ratio is used as population age structure change calculation indicatior to reveal that Chongqing is staying in demographic dividend period,computing model is used to analyze the effect of population stucture on investment and economic growth of Chongqing in demographic dividend period and the results show that the population structure has impact on investment and that Chongqing should take the opportunity to harvest demographic dividend to most extent in th eprocess of population change.