This year marks the 70th anniversary of the founding of New China. Talking about the 70 years of New China will inevitably involve the understanding of the relationship between the two historical stages of the first 30 years and the last 40 years. This article reviews the actual situation of economic development and the improvement of people's living standards before and after the reform and opening up, as well as the gains and losses in theory and practice, and makes a review and analysis of seeking truth from facts. This paper believes that the two historical stages before and after the reform and opening up are closely linked. Without the standing up and initial strength of the previous 30 years, there will be no prosperity and further strengthening after the reform and opening up.