This paper explores the impacts of the universal two-child policy on Beijing’s population in the long term.It gives a detail estimation of Beijing population considering the latest fertility and immigration policy and can help related government department management population.The cohortcomponent method based on a net migration was applied to project population by age for Beijing from 2020 to 2050 in four fertility scenarios.The innovation is the estimation method of the mortality rate with the life table linked with life expectancy.The results show that,though the basic development trend of Beijing’s population will not change essentially under the universal two-child policy,low birth rate and aging problems will be improved.Compared with the partial policy relaxation,the total population will be 876,478 persons more than that in 2050,the share of population aged 0-14 will increase 1.1 percentage points,and the aged dependency ratio will decrease 1.96 percentage points.Some measures should be taken to encourage more couples to have a second child and introduce more young talents to promote Beijing’s prosperity.