For the sake of a more accurate shel boundary and calculation of radiation heat transfer in the Directional Solidiifcation (DS) process, a radiation heat transfer model based on the Finite Element Method (FEM) is developed in this study. Key technologies, such as distinguishing boundaries automaticaly, local matrix and lumped heat capacity matrix, are also stated. In order to analyze the effect of withdrawing rate on DS process, the solidiifcation processes of a complex superaloy turbine blade in the High Rate Solidiifcation (HRS) process with different withdrawing rates are simulated; and by comparing the simulation results, it is found that the most suitable withdrawing rate is determined to be 5.0 mm?min-1. Finaly, the accuracy and reliability of the radiation heat transfer model are veriifed, because of the accordance of simulation results with practical process.