Inventorying blood products is an essential process in blood station management. Traditional methods need to integrate barcodes with refrigerators, which suffer from low time efficiency, high error rate and high labour cost. Several methods have been proposed to automate this process in blood stations. However, none of them is ideal enough. In this paper, we analyse the difficulties of automation in blood inventory, and propose an automated blood inventory system based on UHF RFID technology. Comparisons over our method with manual inventory and handheld RFID inventory are conducted. The result shows that our method is nearly 10 times higher than manual inventory in time efficiency while increases the accuracy to 100%.