Abstract: The critical rod position search of the core is an important part of the nuclear reactor core physical design. The traditional linear interpolation method needs much iteration when searching the critical rod position, which is inefficient and takes long time. A rapid critical rod position search method based on control rod value function was proposed in the paper. The function relationship between the control rod value and the rod position was obtained and applied to the 3D core physical code PBRT. Compared with the linear interpolation method, it is found that the critical rod position of the control rod value function method meets the critical search convergence criteria, and the search efficiency is improved obviously. It is a reasonable and feasible fast search critical method.