When drilling in complex reservoirs,gas will cut the borehole by gravity substitution effect、underbalanced gas cut way and so on.the existing gas cut detection methods are mainly mud pool level monitoring,outlet flow detection and gas invasion acoustic time monitoring methods,but these methods have low gas cut detection efficiency and can not identify the early warning .Based on gas cut early identification difficult problem, considering gas physical properties with temperature and pressure changes,combined with the formation of seepage,a gas cut transient heat transfer and multiphase flow model is established,and the numerical solution method is given. By solving the model, the results show that: in the process of gas cut bottom hole pressure lowering, and with the increase of gas cut time bottom hole pressure decrease rate is accelerated,meanwhile,bottom hole temperature rising,annular outlet temperature decreases. According to these rules,a new method for early detection of gas cut is proposed through combining bottom hole pressure and wellhead temperature or bottom hole pressure and bottom hole temperature.