A solution based on surface acoustic wave(SAW) tag is proposed for the parallel detection of soil temperature and moisture. The coupling-of-mode(COM) theory is used to model and simulate the impedance-loaded SAW tag, and the variation of the echo amplitude and phase of the load reflector with the capacitance value is obtained. On this basis, a dual channel double-sided tag structure is designed according to the different sensing mechanisms of SAW tag to soil temperature and moisture. The use of time-division multiple access(TDMA) method solves the problem of echo signal aliasing during detecting soil at different depth levels simultaneously. The soil temperature and moisture detection is implemented through the phase and amplitude ratio of the echo signal. The tag is tested using a vector network analyzer and a reader, and the test results show the effectiveness of the tag.