This paper elicits Phased Array Radar Beam Bound by using Differential Coefficient method, then, compares it with the connection between the measure of phase Shifter and the HPBW, and simultaneously puts forward a selecting standard of Phase Shifters' digit. Finally, the paper analyzes the effect of different Phase Shifters' Digit on the Beam Coverage degree, imitates and compares the Pattern of Beam Scan, which validates the rationality and applicability of it.