Abstract: A mathematical model was established in this paper to deduce unknown surface temperature and surface heat flux density in the process of 1-d unsteady state thermal conductivity based on the temperatures measured at each internal temperature measuring point in casting strand.Difference equation for each node was established by using heat balance method,and through the introduction of sensitivity coefficient,the initial boundary conditions was optimized through Newton iterative method.In order to verify the correctness of the mathematical model,through exerting heat flux with given density on the solid surface,it was found that the heat flux density obtained through deduction coincided with the given value.In addition,the changing rule of the heat flux density on the surface of the casting strand in the process of secondary cooling during continuous casting was analyzed.