Forest fire is one of the most important ecological process that drives the regeneration,succession and material circulation of boreal forests.The aboveground and surface soil biomass and carbon density of boreal forests were significantly changed by forest fire.Subsoil carbon pool,which may store almost half of soil carbon of boreal forest,is also strongly influenced by forest fire,however,was paid little attention to.In this study,we measured effect of fire on subsoil carbon density,and analyzed relationship between subsoil carbon density and its driving factors in a 2010 burned site at Huzhong Natural Reserve in Great Xing’an Mountains.Results showed that the distribution of soil organic carbon(SOC)content along depth in burned sites were significantly different from that of unburned control sites,deep SOC content and carbon density in burned sites were significantly lower than that in the control sites(n=56,P<0.001);microbial biomass carbon content and easily oxidized organic carbon content in burned sites were significantly higher than that in control sites(n=56,P<0.01),but soil C/N and dissolved organic carbon content were significantly lower than that in control sites(n=56,P<0.01).Soil moisture in burned sites was significantly lower than the control(n=56,P<0.001),but soil temperature and pH were significantly higher than those in control sites(n=56,P<0.001).Our results suggested that forest fire significantly reduced chemical stability of subsoil SOC of boreal forests,promoted the growth of soil microorganism by increasing soil temperature,and eventually led to the accelerated decomposition of SOC and the decrease of subsoil SOC storage.