The PCR technique has been set up for nearly twenty years and is becoming more and more ripe. But because of the multiple influencing factors and complicated reaction procedures,no mathematical method that can describe the PCR reaction has been given. On the basis of its elementary principle,we suggested a kinetic equation to describe the reaction procedure,Wamp=[Ntarg x (1+P)n1+0.5 x Cenz x U x P x Ceactive x (n-nl)-Ntarg x (1+n x P)] x Cu x M. This equation can describe correctly the accumulation rule of PCR product and thus build up the kinetic-mathematical model of PCR reaction. The predicted CT value of PE 7700 by the kinetic-mathematical model was in accordance with the real value detected by the machine. This kinetic-mathematical model accompanied by proper detecting equipment and computer could make an automatic PCR instrument, which would produce much better result. A laboratory can predict the amount of PCR product by this model and provide accurate information for further handling of PCR product according to its own condition. In this model,the molecular basis that PCR reaction is doomed to change from exponential amplification to linear amplification had been clarified.