Abstract: The influence of the ratio between oxygen contents and free carbon contents(O/C_free ratio for short)in YT hard metal compacts before vacuum sintering and also the influence of compound carbon content in products by vacuum sintering compacts with different O/C_fee ratio at 1250 C for 90 min on the bending strength, hardness and cutting coefficient of YT hard metal are studied in present paper.The results have demonstrated that the carbon contents and strength decrease and the hardness and cutting coefficients increase with the increase of O/C_fee ratio in compact before sintering. The above results reflect on a decarbonization reaction which has happened during sintering.The optimal O/C_free ratio is 1.1~1.5.The method for controlling O/C_free ratio and for calculating composition are also explained.