In this paper, a series of derivatives were synthesized by introducing the pharmacophore pyrazole ring and piperazine ring into the structure of the natural product myricetin through an amide bond. The structures were determined using carbon spectrum and hydrogen spectrum high-resolution mass spectrometry. Biological activities of those compounds against bacteria, includingXac(Xanthomonas axonopodis pv. Citri),Psa(Pseudomonas syringae pv. Actinidiae) andXoo(Xanthomonas oryzae pv. Oryzae) were tested. Notably,D6exhibited significant bioactivity againstXoowith an EC50value of 18.8 μg/mL, which was higher than the control drugs thiadiazole-copper (EC50= 52.9 μg/mL) and bismerthiazol (EC50= 69.1 μg/mL). Furthermore, the target compounds were assessed for their antifungal activity against ten plant pathogenic fungi. Among them,D1displayed excellent inhibitory activity againstPhomopsissp. with an EC50value of 16.9 μg/mL, outperforming the control agents azoxystrobin (EC50= 50.7 μg/mL) and fluopyram (EC50= 71.8 μg/mL). In vitro tests demonstrated thatD1possessed curative (60.6%) and protective (74.9%) effects on postharvest kiwifruit. To investigate the active mechanism ofD1, its impact on SDH activity was evaluated based on its structural features and further confirmed through molecular docking. Subsequently, the malondialdehyde content ofD1-treated fungi was measured, revealing thatD1could increase malondialdehyde levels, thereby causing damage to the cell membrane. Additionally, the EC50value ofD16onP. capsiciwas 11.3 μg/mL, which was superior to the control drug azoxystrobin (EC50= 35.1 μg/mL), and the scanning electron microscopy results indicated that the surface of drug-treated mycelium was ruffled, and growth was significantly affected.