Plant diseases caused by pathogenic fungi or oomycetes seriously affect crop growth and the quality and yield of products. A series of novel 1,2,4-triazole derivatives containing carboxamide fragments based on amide fragments widely used in fungicides and the commercialized mefentrifluconazole were designed and synthesized. Their antifungal activities were evaluated against seven kinds of phytopathogenic fungi/oomycete. Results showed that most compounds had similar or better antifungal activities compared to mefentrifluconazole's inhibitory activity against , especially compound (92%), which possessed outstanding activity. Compound (EC = 13.095 μg/mL) showed a better effect than that of mefentrifluconazole (EC = 39.516 μg/mL). Compound (90%) displayed outstanding anti-oomycete activity against , with an EC value of 17.362 μg/mL, far superior to that of mefentrifluconazole (EC = 75.433 μg/mL). The result of molecular docking showed that compounds and possessed a stronger affinity for 14α-demethylase (CYP51). This study provides a new approach to expanding the fungicidal spectrum of 1,2,4-triazole derivatives.