Researching the past empirical studies, we find that the empirical results of using data from the same or similar stages of economic development tend to be very close; however, there will be some discrepancies when comparing the empirical results of data samples at different stages of development. In order to explain this phenomenon, a theoretical analysis is made on the regional differences in the impact of population ageing on national saving. By analysing the areas considered in this paper as being in different stages of economic development, the combined effects of population ageing on the national saving rate are different. In order to verify the above conclusions, the thresholds and threshold effects are estimated and tested through the threshold model. The results show that the impact of population ageing on the savings rate will be different due to different levels of economic development. When per capita income is below the threshold of 9001.69, population ageing has a greater negative impact on the national savings rate. When per capita income is above the threshold of 9001.69, the negative impact of population ageing on the national saving rate is smaller.