Degradation dynamics and residue of 19% triforine emulsifiable concentrate in soil and watermelon of Guangdong and Guangxi province were investigated by gas chromatography. The results showed that the limit of detection established was 0.005 ng, and the lowest limit of quantification of the proposed method was 0.005 mg/kg in soil and 0.010 mg/kg in watermelon. The average recovery of soil ranged from 71.81% to 101.45% with a relative standard deviation (RSD) of 2.27% to 3.59%; and that of watermelon ranged from 77.63% to 100.23% with a RSD range from 4.08% to 10.43%, which fitted with the first-order kinetics exponential equation. The half-life of triforine in soil from Guangdong and Guangxi were 4.12 d and 4.52 d, respectively, and that in watermelon were 1.81d and 1.90 d, respectively. Triforine, which belonged to the easily degradable pesticide, declined faster in soil than that in watermelon. It was tested that the residue of triforine in soil and watermelon during harvest were 0.049 9–0.682 2 mg/kg and 0.028 5–0.514 1 mg/kg respectively under the 3–4 of frequency usage at the recommended dosage and at the 1.5 times recommended dosage circumstance, respectively. These residues were below the maximum limit of 1.0 mg/kg in fruits specified by Malaysia government.