Abstract: Rotational motion estimation is essential for MIMO radar imaging with ISAR technique. According to the estimation, the echo data can be rearranged and interpolated, and the cross-range scaling can be implemented for range-Doppler imaging. For an object rotating with a constant acceleration, a method is proposed to jointly estimate the initial rotating velocity and the rotating acceleration. It estimates the phase factors of the difference signal by exploiting the phase difference between the echo signals from two different channels of MIMO radar. Based on this, the errors induced by trigonometric approximation in the derivation of the method are analyzed, and then the influencing factors causing these errors are obtained. Meanwhile, the motion parameter estimation resolutions are assessed quantitatively. Finally, simulations are performed to verify the correctness of the proposed method and the analysis.