Ground-moving-Target indicator (GMTI) has been widely studied and can be formulated into a multiple-input multiple-output (MIMO) radar scenario by taking the advantage of MIMO. Usually, adaptive technique is required for GMTI MIMO radar, which includes space-Time adaptive processing (STAP) and invariance statistics technique (invariance on local ground clutter) as we proposed in this paper. However, GMTI system still suffers from some non-idealities when the adaptive technique is applied. Typically, the model mismatch problem degrades the performance of the adaptive technique. Therefore, the model mismatch analysis of both STAP and invariance technique is investigated in this paper.