To meet the design requirements of the miniaturization and circular polarization of ultra high frequency(UHF) band radio frequency identification(RFID) reader, a novel compact square quadrifilar spiral antenna with righthand circular polarization is presented. The antenna is composed of four invertedF elements printed on the FR4 substrate, and the dimension of the antenna can be effectively reduced by array element bending and the continuous phase rotation method. The improved microstrip powerdivided feeding network and a new coupling match method are used to improve the bandwidth of the axial ratio and gain of the circularly polarized antenna. The proposed antenna has a size of 56 mm×56 mm×8 mm than the reference design reduced by 12.9% to 86%, the 3 dB beamwidth of more than 120°, the peak gain of 2.8 dBic with the axial ratio under 2 dB and the cross polarization of less than -15 dB.