Abstract: To evaluate reduced-dose application control efficacy of common Pinellia ternata fungicides with four kinds of synergists on leaf spot disease, and to screen out suitable products reduction and synergistic effect for Pinellia ternata, field efficacy experiment was carried out by stem and leaf spraying method, and five-point sampling method was used to conduct fixed-point investigation on occurrence of Pinellia ternata diseases．Experiment demonstrated that when Agrospred 109 synergist was added and conventional dose reduced by 20% for controlling Pinellia ternata leaf spot disease, 20 days after second application, control efficacy increased by 3.19% than conventional dose, yield increased by 1.63%, and pesticide residue dose below 0.010 mg/kg．However, when adding Silwet 408, Silwet 819 and Agrospred 910 with a 20% reduction in conventional dose, differences in disease control efficacy and yield increase compared to conventional dose were not significant．Research results showed that in field application, Agrospred 109 could be added to reduce conventional dose by 20% for controlling Pinellia ternata leaf spot disease．