As an important tool of modern agriculture, pesticides are widely used in agricultural production with the advantage of their efficient ability to kill pests and diseases, but they also cause pollution to the environment while killing pests. In this paper, a spectral detection of pesticide spray was carried out to study the real-time monitoring of pesticide use by laser-induced breakdown spectroscopy(LIBS) technology. First, the atmospheric LIBS spectrum in a clean environment was detected. Many atoms emission spectra of nitrogen (N) and oxygen (O) were detected in the air spectrum, which has a good consistency with the air composition. At the same time, two hydrogen Balmer series atomic lines (H_α and H_β) were also observed, which was mainly derived from water vapor in the air. It is worth noting that two Argon(Ar) atomic lines were also found in the air spectra, indicating that the LIBS technology has great potential in detecting trace elements. In this experiment, the pesticide Decis was selected as the research object, and LIBS tested its active ingredient deltamethrin (C₂₂H₁₉Br₂NO₃, CAS: 52918-63-5). The halogen element bromine(Br) was observed in the spectra of deltamethrin, and two Br atomic emission lines (827.294, 833.470 nm) were marked. During the detection of pesticide samples, many characteristic spectral lines that did not appear in the air spectrum were also found, including CN molecular band and C₂ molecular band. What are more, elements natrium(Na) and calcium(Ca) that were not observed in the air spectra were also detected. Especially for Ca, the intensity and number of spectral lines in pesticides significantly increase. Finally, the temperature of the CN molecule was studied. The vibrational temperature of CN molecule in deltamethrin and pesticide were estimated to be 8 800 and 6 200 K respectively, and the rotational temperature to be 8 600 and 5 500 K respectively. The above results indicated that it is feasible to use LIBS technology to monitor pesticides online, and LIBS technology has a promising future in pesticide monitoring.