The information of soil environment is one of the most important information parameters in precision agriculture. There are some disadvantages lie in current wireless sensor networks in agriculture, including longtime monitoring, environmental protection and tracking ability. According to these disadvantages, a novel wireless monitoring method was proposed based on radio frequency identification (RFID) sensor tag. The RFID sensor tag was based on ultrahigh frequency (UHF) electronic product code (EPC) 2nd generation communication protocol and worked on a passive mode. A new method of data fusion was also proposed. Compared with the traditional data fusion method, the power consumption and response time of the system were significantly reduced. Because of the complex composition of farmland soil, the loss of electromagnetic wave transmission in farmland soil and the basic conditions for the normal work of the tag were determined. In view of the fact that the transmission accuracy of sensor labels was insufficient when the embedding depth was more than 30cm, two sensor tags at the same measurement point were proposed, and higher data transmission accuracy was obtained through the polarization direction of antennas. The communication performances and the temperature and humidity performances of the proposed sensor tag were tested in laboratory. The experimental results showed that the proposed sensor tag exhibited good consistence with conventional methods. The maximum error of the temperature test was not more than 1.5%, and the maximum error of the humidity test was not more than 1%. Compared with the existing soil environment monitoring methods, it had the advantages of convenience, low cost, long life and rapid positioning.