Abstract: To overcome the larger deflection of angle measurement, existing in subarray division of large arrays, weight optimization and the monopulse angle estimation, the large number of arrays, the weight approach algorithm and the large bias of the target departing more than 3 dB from the antenna, a 4-channel monopulse angle measurement method was proposed based on dimensionality reduction of phased array with an additional delt-delt channel. Combining the particle swarm optimization algorithms and weight optimization algorithm, the 4-channel monopulse angle measurement method was designed to greatly decrease the number of the channel, reduce project implementation difficulty and keep fine beam shape, to improve the monopulse angle estimation and the angle measurement accuracy of the beam departing more than 3 dB from the antenna, and to improve the efficiency of angle estimation and reduce the loss of angle measuring range. The simulation results and performance analysis show the effectiveness and feasibility of the presented algorithm.