Abstract: A 3-D space-time nonadaptive pre-filtering approach in airborne radar is proposed in this paper. It makes full use of predictable radar system and platform parameters such as airborne crab, Pulse Repetition Frequency (PRF) and interelement spacing, and the 3-D space-time nonadaptive filter is easily designed by analyzing the structure of the received sampling data of two adjacent pulses. Most clutter is filtered previously so that small part of residual clutter can be sufficiently suppressed by reduced-dimensional adaptive processing. The simulation results confirm that the proposed pre-filtering approach is compatible with airborne crab and can reduce the Degree of Freedom (DoF) of clutter, and the moving target detection performance is improved in the whole clutter region, especially in mainlobe region.