Abstract: To address the urgent challenges of radar mainlobe active composite jamming in electronic countermeasures, a method for anti-mainlobe composite jamming based on space-time-polarization multi-domain blind source separation is proposed. First, a joint space-time-polarization receiving signal model is constructed to exploit the differences between target and jamming in three dimensions: In the spatial domain, a polarization sensitive array is utilized to capture directional information of signals and distinguish the direction of arrival between target and jamming through array geometry; in the temporal domain, amplitude and phase differences of signals between adjacent pulse repetition intervals are leveraged; in the polarization domain, orthogonal dipole antennas are employed to extract polarization scattering characteristic differences between target and jamming. Then, the joint approximate diagonalization of eigen-matrices blind source separation algorithm is adopted to separate target and jamming into distinct channels. Finally, target echoes are identified through matched filtering. Simulation results demonstrate that the proposed method effectively suppresses composite jamming composed of self-protection dense false-target jamming and escort blanketing jamming, with superior performances in output signal-to-interference-plus-noise ratio and similarity coefficients compared to the existing blind source separation-based anti-mainlobe jamming methods.