A mathematical model of the inverse heat transfer problem of blast furnace lining is established in this study. Following the identification of the boundary conditions of the model, the inverse problem via the conjugate gradient method was decomposed into three issues: the direct problem, the sensitivity problem, and the adjoint problem. The feasibility of the model was verified through two types of real inner wall boundary shape functions. The effects of the initial inner wall boundary shape function and the number of measuring points are also investigated. Results showed that the accuracy of the inverse solution is independent of the initial inner wall boundary shape function. The number of measuring points exerts some influence on the inversion results. That is, a large number of measuring points equates to a good capture of curves, but an accurate inverse solution also can be obtained with few measuring points, although arranging a large number of points can achieve a slightly better solution. The average relative error of this solution is approximately 3%.