Abstract: The deceptive mainlobe jamming of airborne radar not only causes a large amount of false alarms but also contaminates samples of the Space-Time Adaptive Processor (STAP). Hence, the performance on clutter suppression is degraded and signal self-cancellation occurs due to the distorted adaptive pattern. A polarization-space adaptive beamforming algorithm utilizing the polarization difference between the target signal and jamming is proposed for suppressing the deceptive mainlobe jamming. Firstly, the eigen-fusion based jamming covariance matrix is estimated by the samples obtained from clutter-free Doppler zone. Then, the polarization-space adaptive beamforming algorithm is carried out via synthesizing subarrays with overlapped window. This algorithm has the ability to suppress mainlobe jamming and retain the spatial degree of freedom for clutter suppression. Finally, the STAP is utilized to suppress the residual clutter. The proposed method can efficiently suppress the dense deceptive jamming, and hence, reduce the number of false alarms. The performance of STAP for clutter suppression can also be improved. Simulation results verify the effectiveness of the proposed method.