Using ( 0,0) mode of the unloaded microstrip antenna analysed shorting post rectangular microstrip patch antenna, deduced the calculating formula of input impedance, and the calculating results were illustrated. 用未加载微带天线的(0,0)模分析了含短路针的矩形微带贴片天线,推导了输入阻抗的计算公式,给出了计算结果。