In order to realize the detection of heavy metal Pb2+ in soil, the content of heavy metal Pb element in soil was detected by terahertz spectroscopy. The relationship between spectral absorption rate and Pb2+ content in soil was analyzed. A basic method for the detection of heavy metal content in soil by terahertz technology was provided. The soil samples with a certain concentration gradient (30~900mg/kg) were produced by sample holder method and pressedslice method. The spectral data of terahertz transmission soil were collected and preprocessed, including smoothing, multiple scatter correction and baseline correction. The model of heavy metal Pb2+ element in soil samples was established by using the method of full spectral, interval partial least squares and genetic algorithm, respectively. The results showed that the model established by sample box method and genetic algorithm method was the optimal one. The correlation coefficients of calibration set and prediction set were 0.86 and 0.81, root mean square errors of calibration set and prediction set were 23.55mg/kg and 39.52mg/kg, respectively. This research provided a theoretical and methodological reference for important parameters detection of farmland soil using terahertz and the preliminary applications research of terahertz.