Common prosperity is the essential requirement of socialism，and achieving common prosperity for all the people is an important goal in the new era. There is a relatively obvious urban-rural gap within Beijing now，which is an important obstacle for Beijing to achieving common prosperity. The evolution of the urban-rural gap in Beijing was analyzed from three aspects：the gap between disposable income of urban and rural residents，the gap between rural collective economic development in different regions，and the lack of momentum for sustainable development of rural areas in some regions. According to the analysis，the main reasons for the large gap are that the radiation of the service-based industrial system is weak，the siphon effect of central cities still exists，and the contradiction between ecological protection and industrial development is obvious. Therefore，it is necessary to take the opportunity of building a modern metropolitan area in the capital to build a super-large core city and small and medium-sized towns for joint development，and let the polycentric urban system drive the overall regional economic level of Beijing，narrow the current urban-rural development gap，and help achieve common prosperity.