Abstract: The anti-jamming method via block matrix has been analyzed for array jamming suppression. This method firstly blocks the mainlobe jamming signal, then accomplishes anti-jamming process by adaptive beamforming (ABF), whose performance is still lack of detailed analysis. This paper deduces the algorithm implementation principle, introduces anti-jamming equivalent weight vector and analyzes the anti-jamming performance via the array output signal to interference and noise ratio (SINR) gain index and anti-jamming beam pattern. Finally, simulation results show that for the mainlobe jamming suppression, the block matrix method will suffer much distortion (high sidelobes and distorted mainbeam) and loss of array effective aperture, having worse performance than ABF.