A transposition pose calibration method integrating scale factor is proposed for the problem of scale difference in the combined optical scanning system. The mathematical model of the combined optical scanning system is established. Then, the changing trend of global measurement accuracy relative to scale difference is explored based on the numerical simulation. The calibration model of transposition pose considering the scale factor is established. With the Kronecker product expansion, the theoretical solution of the transposition pose is given. The system parameters and scale factors are optimized. The effectiveness and accuracy of the calibration method are verified by simulation and experiment. The results show that the combined positioning accuracy is better than 0.1 mm; the transposition pose considering the scale factor significantly improves the overall scanning accuracy of the combined optical scanning system.