In this paper, assumptions of IPCC five shared socioeconomic pathways are used to project future population and economy in the Belt and Road countries under the Sustainability road (SSP1), Middle of the road (SSP2), Regional Rivalry (SSP3), Inequality road (SSP4), and Fossil-fueled Development road (SSP5). The projected population and economic development scenarios could support the studies on climate change impact, risk, adaptation and mitigation. The results show that: (1) population and GDP in the Belt and Road countries made up 62.3% and 31.2% of the world total in 2016, respectively. The Southeast Asia and South Asia along the 21st-Century Maritime Silk Road show large economic aggregate but low GDP per capita due to their highdensity population. The Central Asia, West Asia, Eastern Europe and other regions along the Silk Road Economic Belthave sparsely distributed population and relatively developed economy. (2) Population and economy in the Belt and Road countries will increase overall in the future, but trends are significantly influenced by social economic policy. Under SSPs, population will increase 0.33 billion (SSP5) -1.83 (SSP3) billion and economy will grow to 3.0 (SSP3)-6.4 (SSP5) times in 2060 with relative to 2016. The percentage of population in the Belt and Road countries to the world total will decrease, but that of GDP will increase in the future. (3) In the mid- 21st century (2051-2060), there will be 95 people and US$1.64 million GDP per square kilometer averaged over the Belt and Road countries, but differences in the projected population and economy among SSP1-SSP5 are obvious. The population in most countries will grow rapidly but the economy will develop slowly under SSP3, but trends are quite the contrary under SSP5. More than half of the countries' GDP per capita will be above US$25 thousand under SSP5, while that at most countries will less than US$20 thousand under SSP3. Changes of population and economy for the SSP1, SSP2 and SSP4 will between the SSP3 and SSP5.