Multiband terahertz metamaterial absorbers are important photonic components responding to, manipulating and modulating terahertz waves. A multiband terahertz metamaterial absorber is constructed based on a periodically split ring resonator structure. Simulations and experimental tests show that the metamaterial absorber exhibits near-perfect absorption of incident terahertz waves at 0.918 THz and 1.581 THz in the Transverse Magnetic(TM) polarization case. Based on the dielectric sensitivity of the resonant absorption peaks of the device, the sensing performance of the metamaterial absorber is investigated after loading four kinds of pesticide solution with different concentrations of carbendazim, tricyclozole, paraquat, and thidiazuron, and the detection sensitivities of the device for the four kinds of pesticides are obtained as 1.06 GHz/ppm, 0.65 GHz/ppm, 0.67 GHz/ppm, and 2.07 GHz/ppm, respectively. The results show that the device can achieve the sensing detection of trace pesticides, which provides a new idea for future food quality and safety control.