To meet the requirement of intelligent development of pig breeding industry, solve the problem of low weighting efficiency and rely on artificial, an automatic weighing system based on RFID was designed. In this paper, radio frequency identification technology was introduced in the weighting system, the automatic identification of the pig's identity and the measurement of the body weight in the case of unattended were presented. A kind of switching door controlled by PLC was designed to ensure that pigs are not affected by other pigs. Using Ethernet transmission technology to achieve the transmission of relevant data. The results of the experiment show that the system can quickly and accurately measure the weight of pigs, the measurement error is less than 0.05kg. Compared with the traditional weighing system, this system can improve the weighing efficiency, reduce the cost, promote the development of pig breeding industry.