This paper presents an overview on progress in the development of the Beijing Climate Center Climate System Model (BCC_CSM)and its four components:atmosphere,land surface,ocean and sea ice.It focuses on the two recent versions,i. e.,BCC_CSM1.1 with a coarse atmospheric resolution (approximately 2.8125°*2.8125°)and BCC_CSM1.1(m)with a medi-um atmospheric resolution (approximately 1.125°*1.125°).Both versions of BCC_CSM are fully-coupled climate-carbon cycle models involving terrestrial and oceanic carbon cycle and vegetation dynamics.They can well simulate the atmospheric CO_2 con-centration and its temporal evolution when forced by anthropogenic emissions of CO_2.They contribute to the CMIP5 efforts supporting the IPCC AR5.A large amount of simulations from BCC_CSM1.1 and BCC_CSM1.1 (m)are available for studies on global climate and future climate projection.