Plant viral diseases cause great harm to crops in terms of yield and quality. Natural products have been providing an excellent source of novel chemistry, inspiring the development of novel synthetic pesticides. The Amaryllidaceae alkaloids crinasiadine (), trisphaeridine (), and bicolorine () were selected as parent structures, and a series of their derivatives were designed, synthesized, and investigated for their anti-plant virus effects for the first time. Compounds and exhibited comparable inhibitory activities to ningnanmycin against tobacco mosaic virus (TMV). Preliminary research into the mechanism, involving transmission electron microscopy and molecular docking studies, suggests that compound may interfere with the elongation phase of the TMV assembly process. This study provides some important information for the research and development of agrochemicals with phenanthridine structures.