By analyzing the composition of the population group in terms of age and gender, the author comes up with a short life table using the data of the sample death rate in 2003, applying the method proposed by Qinglang Jiang. The life expectancy of the current population is also estimated. Thereafter, the author continues with analyzing the change of the life expectancy in the whole population from liberation to present, as well as suggesting possible reasons that might have resulted in these changes. In the end, the life expectancy of the whole population in our country from 2001-2020 is predicted, using the fourth and fifth nationwide census data. We get a conclusion in the end that the life expectancy will continue to grow but the growth rate will decrease annually.