Acetamiprid is a chloropyridine neonicotinoid insecticide that is one of the most commonly used pesticides due to its binding selectivity toward the nicotinic acetylcholine receptor of insects. To understand the relationship between the fingerprint feature and the corresponding structural information in the terahertz region, experimental and theoretical investigations of the terahertz absorption spectrum of acetamiprid crystal were carried out using the terahertz time-domain spectroscopy (THz-TDS) and density functional theory(DFT). The terahertz absorption spectrum of acetamiprid was measured in 0.3~3.3 THz frequency range at room temperature by the THz-TDS system. A number of characteristic absorption peaks in this range were observed at 1.08, 1.38, 1.97, 2.54 and 2.89 THz, respectively, which can be the THz fingerprint spectrum for detecting acetamiprid. To better understand the experimental absorption spectrum's theoretical mechanism, calculations based on density functional theory were performed to analyze the isolated molecule and unit cell of acetamiprid. The geometry optimization and frequency calculation of the isolated molecule model was performed using DFT with periodic boundary conditions employing the B3LYP hybrid functional with the 6-311G(d,p) basis set. Some differences were observed between the simulation results and the experimental data, which means that the isolated molecule simulation has some limitations. The theoretical calculations of the unit cell were performed based on the solid-state DFT using the CASTEP program, a part of Materials Studio 8.0 from Accelrys. The calculations were performed on the crystalline state within the generalized gradient approximation (GGA) at PW91, PBE, PBEsol and WC correlation functions. The calculated structural data of bond lengths and bond angles for acetamiprid molecule and unit cell were compared with -X-ray diffraction values(XRD). Among these calculations, PBE simulations provide a significantly similar tendency with the XRD experimental values. And the calculated THz spectrum of the PBE provides better agreements with observed THz spectral characters. Consequently, the observed spectral features were assigned according to the results of the PBE simulation. The study indicates that acetamiprid's characterized features primarily originated from intermolecular collective vibrational modes, which were dominated by hydrogen bonds such as C—H…N.