The number of permanent residents reached 21.707 million last year, 22,000 fewer than the previous year, Xinhua said.
The number of people in the city's six urban districts fell 3 percent from 2016 to 2017, the Xinhua report said, citing the city's People's Congress.
Authorities in Beijing have been trying to curb population growth as part of their efforts to ease traffic congestion, resource shortages and house price inflation.
Beijing's population has risen by two-thirds since 1998, while energy consumption has more than doubled and the number of vehicles tripled. It said in 2016 it would try to cap its population at 23 million by the end of the decade.
The city has been working on integrating its economy with the neighboring province of Hebei and the city of Tianjin in a bid to allow some of its universities, government departments and industrial firms to move out.
It has also set up a new development zone at Xiongan in Hebei to take on some of Beijing's "non-capital" functions, and it is also investing heavily on transportation networks in order to make it easier for long-distance commuters.
While big cities like Beijing and Shanghai have sought to control population growth, China as a whole is trying to boost its birth rate, which fell in 2017 and is expected to decline further this year.
China's elderly population is expected to reach 400 million by the end of 2035, up from around 240 million this year, putting its health services and pension funds under immense strain, according to data published last year by the China Association of Social Security, a research group.