1,2,3-Thiadiazoles, an important synthetic active substructure, are nowadays becoming one of the important branches in novel pesticide development. To develop pesticide candidates with diverse biological activities and probe their structure-activity relationship, three series of 5-methyl-1,2,3-thiadiazoles were rationally designed and synthesized using a simple and convenient one-step synthetic procedure via Ugi reaction. Biological activities of the target compounds including fungicidal activity, antivirus activity in vitro and in vivo, and systemic acquired resistance were systematically evaluated. The results indicated that compound III(10) showed broad-spectrum of activities against most fungi tested, and compounds I(10) and II(17) showed excellent potential antivirus activities as compared to positive control agent ribavirin. The preliminary structure-activity relationship was also discussed. The results of these studies indicated that the 5-position-substituted 1,2,3-thiadiazoles exhibited good antivirus activity and were worthy of further study in pesticide development.