In this study, in order to solve the problems of low sensitivity and complex sample pretreatment in traditional detection, a method was proposed to detect plant growth regulators using terahertz combined with metamaterial sensors. Two metamaterial sensors with different structures are designed. The differences of two kinds of metamaterial sensors for detecting plant growth regulators were analyzed from three aspects of frequency domain, time domain and absorption characteristics. It is further proved that the difference of metamaterial structure will lead to the change of frequency shift, time domain waveform and absorption characteristics of measured samples, and the influence of sample concentration on the detection characteristics of the metamaterial sensor. The results show that both metamaterial sensors can effectively detect the four plant growth regulator solutions with concentrations as low as 0.05 mg/L. In terms of detection and sensing, the frequency shift, sensitivity, figure of merit value, vibration amplitude and change rate of absorption intensity of metamaterial sensor 2 are higher than each parameter of metamaterial sensor 1, which has better detection performance. However, in terms of identification between samples, metamaterial sensor 1 is more suitable for the identification of daminozide and naphthaleneacetic acid solutions, and metamaterial sensor 2 was more suitable for the detection of glyphosine and gibberellic acid solutions. It provides a new method for multi-target fusion to detect plant growth regulators with high sensitivity and high accuracy.