This paper presents a joint method of Doppler Beam Sharpen (DBS) imaging and Signal Subspace Processing (SSP) to achieve Ground Moving Target Indication(GMTI) for alongtrack dual-antenna airborne radar. When the error of the two antennas (also refers to channels)changes pulse to pulse, the method SSP is used to precisely calibrate the two antennas DBS images, then to deject the ground moving targets in the difference image of the two calibrated images. The method DBS-SSP is proved to offer performance improvement on the actually measured data and simulated data.