In order to study the dynamic influence mechanism of population characteristics on health expenses, the panel data of 31 provinces, autonomous regions and municipalities directly under the Central Government (excluding Hong Kong, Macao and Taiwan) from 2009 to 2016 were used to construct panel smooth transformation model with population characteristics as heterogeneous variables for empirical analysis. The results show that the population number, population structure and population distribution have significant nonlinear effects on per capita health expenses, and the threshold values of population number, population structure and population distribution are 24.6686 million people, 6.9928%, 40.707%. When the threshold is crossed, The effect of population size on per capita health costs is reduced smoothly, The effect of population structure and population distribution on per capita health cost changed from inhibition to promotion.Therefore, according to the relationship between current population characteristics and health expenses, all regions should optimize the structure of health expenses expenditure, improve the level of health services, especially expand the scale of education and training of targeted rural medical students, strengthen the education and training of rural doctors, in order to narrow the difference between urban and rural diagnosis and treatment level.