Control of plant virus disease largely depends on the induced plant defense achieved by the external application of synthetic chemical inducers with the ability to modify defense-signaling pathways. However, most of the molecular mechanisms underlying these inducers remain unknown. Here, we developed a lentinan-loaded hydrogel with the core-shell structure and discovered how it protects plant from different virus infections. The hydrogel was synthesized by adding a chitosan shell on the surface of the sodium alginate-calcium ion-lentinan (LNT) hydrogel (SL-gel) to form CSL-gel. CSL-gel exhibits the capacity of prolonging the stable-release of lentinan and promoting calcium ions release. Application of CSL-gel on the root of plants significantly promotes plant growth and development and induces broad-spectrum resistance against TMV, TuMV, PVX and TRV. Furthermore, we found that the sustained release of calcium ions from the CSL-gel triggers the high expression of cal-modulin-like protein 30 (CML30), and silencing of CML30 enhances the susceptibility of tobacco to TMV. Our findings provide evidence that the novel and synthetic CSL-gel with the sustainable release of LNT and calcium ion strongly inhibits the plant virus infection. This study uncovers a novel mode of action by which CSL-gel with the stable release of calcium ion triggers CML30 expression.