The final residue experiment of diflubenzuron in citrus(Citrus reticulata Balanco) was carried out in twelve cities(Changsha, Zhangjiajie, Lanxi, etc) in China in 2018. And the residue dissipation dynamics experiment of diflubenzuron was studied in Changsha, Gaoan, Nanning and Zhangzhou. The residue of diflubenzuron in citrus whole fruit and pulp were investigated by high performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS) method, and then the risk assessment for dietary safety risk of diflubenzuron in citrus was studied based on the residue data. The results showed that citrus samples were first extracted with acetonitrile ultrasonically, then purified by PSA and anhydrous magnesium sulfate, and finally detected by HPLC-MS/MS, the external standard method was used for quantification. The average recoveries of diflubenzuron in citrus whole fruit and pulp at the spiked level of 0.01, 0.10, 1.00 and 5.00 mg/kg were 89%-102% and 76%-99%, respectively; and the relative standard deviations were 7%-11% and 8%-9%, respectively. The limits of quantitation of diflubenzuron in citrus whole fruit and pulp were both 0.01 mg/kg. The residues of diflubenzuron in citrus whole fruit and pulp decreased slowly over time. The dissipation half-lives of diflubenzuron in citrus whole fruit and pulp were 13.0-18.0 d and 9.6-34.0 d, respectively. The mass fraction 25% wettable powder of diflubenzuron was sprayed at doses of 125 mg/kg(2000 times of the liquid) for 3 times on citrus with an interval of 7 d. Then samples were collected and determined at 35 days after the last application. The residues of diflubenzuron were <0.01-0.55 mg/kg in citrus whole fruit and <0.01-0.93 mg/kg in citrus pulp, respectively, which were both lower than provisions of maximum residue limit(1 mg/kg). The result of dietary safety risk assessment revealed that the national estimated daily intake of diflubenzuron were 0.651 2 mg in citrus whole fruit and 0.644 4 mg in citrus pulp, accounting for 51.7% and 51.1% of the acceptable daily intake respectively, which indicates a low risk from long-term dietary intake in the general population.