Some batches of exported Chinese tea have been found to contain lufenuron residues exceeding the permitted levels, whereas the current national standard lacks a maximum residue limit for this compound. To clarify the residue behavior and dietary risk during tea cultivation and processing, a field trial was performed in Shaoxing, Zhejiang Province. An analytical method for the determination of lufenuron residues in different tea matrices was established using a modified QuEChERS pretreatment method coupled with high-performance liquid chromatography–tandem mass spectrometry. Good linearity (R² > 0.99) was achieved for lufenuron in the concentration range of 0.005–2 mg·L?¹. At three spiked levels of 0.05, 0.5, and 5 mg·kg?¹, the average recoveries of lufenuron in fresh tea leaves, green tea, and black tea were found to range from 76.46% to 98.26%, with relative standard deviations of 1.33%–5.66%, and the limit of quantification was determined as 0.05 mg·kg?¹ for all matrices. The dissipation behavior of lufenuron in fresh tea leaves was best described by the combined first+first-order kinetics model (R² > 0.99), with a half-life of 7.21 days. During the processing of fresh leaves into finished tea, a concentration effect of lufenuron was observed, with total processing factors of 1.44–2.10 for green tea and 1.59–2.35 for black tea. After dry-weight correction, the fixing and drying steps were identified as the key stages responsible for lufenuron degradation in green tea and black tea processing, respectively, with single-step degradation rates of 29.69% and 35.95%. The chronic dietary risk quotient of lufenuron was calculated as 43.77%, indicating an acceptable level. This study provides a theoretical basis for the rational use of lufenuron in tea plantations.