In the reentry process, the boundary-layer transition (BLT) is a common phenomenon which can cause aerodynamic interference. BLT also leads to attitude oscillations, resulting in positional deviations of the impact point. To estimate the deviation early and make corrections accordingly, in this paper, the Rapid prediction Method for Impact Point of Spin-Inertial Reentry (RPM) is proposed. Firstly, the additional trim angle-of-attack is established to simulate the aerodynamic interference during the reentry process. An equivalent model of BLT interference is established with two variables -transition force and the transition moment. Then, in order to obtain the transfer relationship from external inputs to the velocity angle, the equivalent model is incorporated into the state equations. By simplifying transfer functions, the RPM under the influence of BLT interference is developed. Finally, compared with the results of traditional six-degree-of-freedom simulation calculations, the RPM can accurately calculate the impact point with fewer steps.