Abstract: To investigate the environmental behavior of the novel fungicide fluindapyr in the soil–leaf lettuce system under earthworm mediation and its effect on leaf lettuce quality, a pot experiment was conducted with a two-factor treatment consisting of fluindapyr exposure and earthworm inoculation. Four concentration levels of fluindapyr (0, 0.2, 1.0, 5.0 mg/kg) and two treatment levels of earthworms (0, 15 individuals per pot) were employed. After 56 days of exposure, the residual rate of fluindapyr in soil and the residues in the stems/leaves and roots of leaf lettuce were determined. Meanwhile, the biomass (fresh weight, plant height, root length) and leaf nutritional quality indicators (vitamin C, soluble sugar, carotenoids, soluble protein) of leaf lettuce were measured. The results showed that: 1) Earthworms significantly promoted the degradation of fluindapyr in soil, reducing the residue rates by approximately 10% across all concentration treatment groups compared with the no-earthworm controls, with the strongest promoting effect observed at the lowest concentration (0.2 mg/kg). 2) Earthworms significantly decreased the residual contents of fluindapyr in lettuce shoots and roots, with a reduction of over 30% at the high concentration. However, their effects on plant accumulation of fluindapyr exhibited a concentration-dependent pattern of "promotion at low concentrations and inhibition at high concentrations". 3) The translocation factors (TF) of all treatments were less than 1, indicating that fluindapyr was more prone to accumulate in roots, and earthworms did not alter its translocation pattern in plants.4) Earthworms significantly increased the fresh weight and plant height of leaf lettuce under fluindapyr stress, and effectively alleviated the inhibition of fluindapyr on the growth of leaf lettuce. 5) Earthworms regulated the metabolism of leaf lettuce under the stress of fluindapyr. They reversed the inhibition effects of fluindapyr on soluble sugar synthesis, and further increased the accumulation of vitamin C that induced by fluindapyr stress. This study revealed the multiple positive roles of earthworms in regulating pesticide fate and crop responses in the soil-crop system, providing new scientific evidence for the development of earthworm-based green bioremediation technologies to synergistically ensure the safety and quality of agricultural products.