In this study, QuEChERS technology combined with UPLC-MS/MS was used to detect the active ingredients of 33% λ-cyhalothrin-imidacloprid suspension in citrus. Residue and degradation dynamics of the compound in citrus field residue test was studied for the first time. The residual digestion of λ-cyhalothrin and imidacloprid on whole fruit of citrus accorded with the first-order kinetic relationship, and correlation coefficient was 0.956 0～0.992 3. The half-lives of imidacloprid are 5.5～7.6 d while λ-cyhalothrin are 8.2～9.8 d, final degradation rate is above 92%. The terminal residues indicated that the amounts of final residues was positively correlated with the dosage, the number of application and the interval of harvesting. The residues of the two were mainly distributed in peel, followed by whole fruit and pulp. About 28 days later after the last application, the residues of imidacloprid and λ-cyhalothrin in fruits was lower than the MRL value specified in GB 2763—2016, and dietary risk assessment showed that risks of residues were acceptabled. Therefore, it is recommended that 33% imidacloprid-λ-cyhalothrin suspension should be applied in 1 000-fold dilution (330 mg/kg) and can be applied up to 2 times in one citrus production cycle with 10-days application interval and 28-days harvest interval.