A conventional 5.8 GHz microstrip rectangular patch antenna for the radio frequency identification (RFID) system was designed. The antenna possesses the radiation patch size of 15.5 mm×11.5 mm and achieves the -10 dB impedance bandwidth of 80 MHz, the minimum return loss of -36.138 dB. On the basis of the conventional microstrip antenna, an improved antenna combined with the complementary splitring resonators (CSRR) defected ground structure was implemented. The antenna′s radiation patch size is 10mm 7.5 mm and achieves the -10 dB impedance bandwidth of 62 MHz, the minimum return loss of -23.574 dB. Compared with the conventional microstrip antenna, the size of the improved antenna radiation patch is reduced by 57.9%. It shows that the effect of miniaturization is obvious and the bandwidth characteristic, the gain characteristic are able to comply with the general requirements of RFID system.