This paper defines the concept of internal balanced development of population with respect to its quantity and quality: in the process of population development,balance and coordination are gradually achieved in both quantity and quality of the components of the population,while the state of balance is temporary,relative and is constantly evolving from a lower level to a higher level of balance.An evaluation model of internal balanced development of population is developed and empirical analysis is conduced for the West China,suggesting that population development level,internal balanced development level and internal balanced sustainable development level are all low in the west region of China despite the fact that there are large differences within the region.