As the dramatic development of the computer and digital signal process techniques, the phase array radar becomes more and more important for many different kinds of military applications. In order to survive in the complicated electromagnetic environment with different kinds of interference, the adaptive digital beamformin is adopted to suppress the interference. In addition, the signal processing is performed at the subarray level in order to save the hardware resource cost. However, the sidelobe power of the antenna pattern dramatically increases since the output power of the noise for each subarray is different. In order to solve this issue, the normalized adaptive method is proposed to maintain the same output power for each subarray. The float round-off error is also analysed for the proposed method. The simulation results show that the proposed method has good performance.