Abstract: In order to measure the dissipation and residues of cyromazine in Agrocybe aegerita and its substrates, 50% cyromazine SP was used as the test agent. The pesticide distribution in Agrocybe aegerita and the dissipation dynamics in its substrates were investigated. The samples were extracted by methanol, purified by high-speed centrifugation after the addition of sodium chloride, determined by LC-MS/MS and quantified by external standard method. The results showed that there was a good linear relationship between the mass concentration and the peak area in the range of 0.002-0.05 mg/L and 0.01-0.2 mg/L, and R² were 0.997 and 0.998, respectively. When the spiked levels were 0.01, 0.1 and 1 mg/kg in the mushroom and its substrates, the average recoveries ranged from 72% to 110%, with RSDs (n = 5) ranged from 2%-6%, which met the inspection requirement of pesticide residue analysis methods. The dissipation of cyromazine in Agrocybe aegerita was in accordance with the first-order kinetic model, and the half-life was 5.46 d. The main residues of cyromazine in substrates were in the upper part, accounting for 65.8%-93.2% of the total residues. The residues of cyromazine in the mushroom were lower than the MRL in the US (1.0 mg/ kg) 3 days after treated by the dosages of 2 289 g a.i./hm² and 1.5 times of that, by manual spraying for 3-4 times, which were between 0.10 mg/kg and 0.17 mg/kg.