Quasi-solid polymer electrolytes (QPE) composed of Li salts, polymer matrix, and solvent, are beneficial for improving the security and energy density of batteries. However, the ionic conduction mechanism, existential form of solvent molecules, and interactions between different components of QPE remain unclear. Here we develop a multispectral characterization strategy combined with first-principles calculations to unravel aforesaid mysteries. The results indicate that the existential state of solvent in QPE is quite different from that in liquid electrolyte. The Li cations in gel polymer electrolyte are fully solvated by partial solvent molecules to form a local high concentration of Li+ , while the other solvent molecules are fastened by polymer matrix in QPE. As a result, the solvation structure and conduction mechanism of Li+ are similar to those in high-concentrated liquid electrolyte. This work provides a new insight into the ionic conduction mechanism of QPE and will promote its application for safe and high-energy batteries.