Abstract: Cacopsylla chinensis is one of the key pests in pear production. The use of entomopathogenic fungi against C. chinensis is an important strategy to reduce insecticide application and achieve green management. This study investigated the pathogenicity of Beauveria bassiana GSSBb1901 strain on C. chinensis, determined the effects of four nicotinic insecticides on spore germination and sporulation, and evaluated the synergistic effect of the combination of B. bassiana and insecticides on C. chinensis. Results indicated that the mortality rates of C. chinensis across different phenotypes and developmental stages increased with higher spore concentrations of GSSBb1901 strain. Susceptibility, in descending order, was as follows: summer-form adults > summer-form nymphs > winter-form adults, with LC₅₀ values of 1.02 × 10⁶, 3.92 × 10⁶, and 2.25 × 10⁷ spores/mL, respectively. The compatibility evaluation results indicated that all tested insecticides showed measurable growth inhibition of GSSBb1901 strain. Dinotefuran exhibited the lowest inhibition rate, while acetamiprid showed the highest. When combined with GSSBb1901 strain spore suspension (5.0 × 10⁷ spores/mL) at 1/10 of the recommended concentrations, all four insecticides exhibited synergistic effects against C. chinensis. Mortality rates decreased in the following order: thiamethoxam (93.33%) > imidacloprid (78.33%) > pyriproxyfen (73.33%) > dinotefuran (73.33%), all exceeding the B. bassiana single agent (71.70%). The corresponding median lethal times (LT₅₀) were 2.67, 2.90, 3.71, 3.86, and 4.73 days, respectively. In summary, B. bassiana strain GSSBb1901 demonstrated strong pathogenicity against C. chinensis, and the combination of thiamethoxam at 1/10 recommended concentration with GSSBb1901 spore suspension (5.0 × 10⁷ spores/mL) showed a significant synergistic effect.