To study the thermal effect on spectral-line shift of spaceborne imaging spectrometer, the relation between spectral-line shift and rigid-body motion of the mirror is analyzed, and the theoretical model, which is verified and corrected by simulation and thermal-optical test, is established to describe the spectral-line shift property. The mathematical model based on linear optics model is established to describe the relation between spectral-line shift and rigid-body motion of the mirror, and the Mont Carlo method is employed to do the verification. The finite element analysis (FEA) method is used to get the rigid-body motion of mirror under different thermal loads. Code V API functions are used, in Matlab environment, to calculate the variation of the spectral line caused by rigid-body motions, and the spectral-line shift property is studied at the same time. The spectral-line shift model is corrected and verified by thermal-optical test. The results show that spectral-line integral deviation without extension and compression under the temperature from 8 ℃ to 28 ℃. Spectral-line shift values obtained by the thermal optical test are well coincident with the ones calculated by theoretical model. The maximum deviation between theoretical analysis and thermal optical test is not exceeding 12%. The new spectral-line shift model, corrected by the test data, realizes a high precision spectral line shift forecasting. The relative error is less than 5% and the absolute accuracy is better than 0.2 pixel.