Regarding the main-lobe jamming suppression algorithm of phased array radar, the paper analyzes various anti-jamming algorithms based on blocking matrix pre-processing (BMP) according to the study of current anti-main lobe jamming technique in the space-time domain, including the weighting coefficient compensation, whitening, diagonal loading and linear constraint combined with diagonal loading beam retention algorithms. Inspired by the covariance matrix reconstruction (CMR) algorithm of eigen-projection matrix preprocessing, the paper combines modified CMR and BMP algorithm to suppress main lobe jamming. The modified CMR can not only be used when the dimension is lost caused by BMP, but also solve the distortion problems such as the main lobe peak offset in the adaptive beam forming synthesis. The biggest advantage of BMP combined with modified CMR algorithm is that its anti-jamming performance is excellent and stable when the sampling snapshot contains the target signal. Meanwhile, the algorithm complexity and the snapshot sensitivity are both in a low level. In the end, the verification results of the measured data also show the superiority of the proposed algorithm when the sampling snapshot contains the target signal.