There is much difference between historical background，causation and process of the demographic transition in B ICS countries and their European counterparts. Especially， the differentiation between the five countries in population efficiency during the demographic transition makes the comparative study of the five countries demographic transition far more significant than the implication of a mere demographic examination. The article examines the process and changes of demographic transition in the B ICS countries，especially the formation of the population trap under the context of straining relationship between population and resources ，and the process，levels and characteristics of demographic transition in a comparative perspective. Based on current status of population changes and dynamic trends in the five countries，demographic factors of international co mpetitive power of the five
countries are discussed. The article maintains that enhancing and keeping China's future international competitive power depends on reversing the trap of population low efficiency ，having thorough top-level design with national strategic height，and achieving the full right for people of democratic reproductive decision- making.