Environmental impact assessment according to traditional methods is evaluated through the variation of soil, water, air and ecosystems. Such monitoring activities require a lot of time and operating costs. In contrast, when using indirect method like demographic assessment and evaluation, such costs can be reduced. This method uses demographic data systems such as population density, urbanization factors, birth rate, death rate, and incidence of occupational diseases, etc. The demographic data system has close linkage altogether in an information system of a given area. In this paper, we calculated the demographic factor, namely Demographic Tension Index (DTI), for Vietnam from 1995 to 2011. The results show that the Vietnam's DTI increased from 1.803 to 3.262, which means the environmental state of Vietnam from 1995 to 2011 are declining rapidly and can tend to become more polluted in the coming years. This demographic assessment method has been applied within Russian Federation, Ukraine, and Belarus, etc., so its scientific influence is not widespread. Moreover, the required data for the DTI calculation should be accurate and reliable.