The performances of UHF (Ultra-High Frequency) RFID (Radio Frequency Identification) systems are affected by multi-path channels． In order to improve the reliability of UHF RFID systems，this paper gives the probability distribution of SNR (Signal-to-Noise Ratio) under the MRC (Maximal Ratio Combining) combiner for the UHF RFID system with Rician distribution in both forward and backward channels，and presents the theoretical descriptions of both outage probability and bit error rate． Then，a prototype of multi-antenna UHF RFID reader is developed，and the system performance affected by receiving antenna number and Ｒician factor is investigated through numerical simulation and practical test． Experimental results show that multi-antenna technology improves the performance of UHF RFID systems effectively，and that the outage probability and bit error rate of UHF RFID systems both decrease as the receiving antenna number increases．