Aerobic composting is an effective way to treat and recycle agricultural waste materials. However,the aerobic composting is a potential source of greenhouse gases to the atmosphere,which closely relates to the global climate change. Therefore,control of carbon loss in the process of aerobic composting should be primarily considered. An experiment was conducted to study the effect of different biochar additions on carbon transformation and carbon loss in composting of pig manure by using static forced-air composting boxes. The results showed that total organic carbon (TOC) in the composts decreased with the increase of composting time. TOC in the treatments with biochar addition increased by 6.69% ~ 20.60% than that of the control treatment. TOC and water-soluble organic carbon (WSOC) exhibited a similar trend throughout the composting. Humus carbon content (HC) first decreased and then increased with composting time. HC in the treatments with biochar addition decreased by 0.39%~ 14.97% with respect to the control treatment. The ratio of humus acid to fulvic acid was proportional to the amount of the biochar added,which indicated that biochar addition was beneficial to pig manure composting. The weight loss rates of the composted materials were 23.51%~ 30.91% at the end of composting,and the carbon loss rates were 20.71%~ 28.85%. The loss rates of weight and carbon were the highest in the treatment with 3% biochar addition,and were the lowest in the treatment with 9% biochar addition.