Aimed at the problems that large number of training requirement and computational load influence lead to a decline in effectiveness of clutter suppression in the airborne MIMO radar, this paper presents an improved reduceddimension method by a thinking of dividing operation into local plot. The received data in the antennaspulse domain is firstly transformed to the beamDoppler domain, and then the number of auxiliary channels on both sides of main channels in time domain and space domain is adjusted. in order to reduce the degree of freedom in time domain, the paper enhances the directivity of beam and improves detection performance. The simulation results demonstrate that the proposed method can dramatically reduce the computational load and training requirement. The result shows that the system improvement factor of the proposed method has an increase of 3 dB compared to the traditional JDL method under the conditions of errors.