To solve the shortage of the application of conventional methods in beam broadening of phased array antennas, this paper has presented a method for beam broadening by constructing an initial phase based on particle swarm optimization (PSO) algorithm and genetic algorithms (GAs). The paper takes an S-band phased array antenna as an example to construct the same initial phase of linear distribution, and optimize the phase respectively by PSO algorithm and GAs to achieve the purpose of beam broadening and make the peak side lobe level (SLL) meet a certain requirement. The MATLAB program analysis shows that PSO algorithm and GAs achieve relatively high performance in beam broadening.