Abstract: In order to overcome the problem of low ionic conductivity in the existing polymer solid electrolyte, the disclosure provides a solid electrolyte, comprising a polymer, a lithium salt and an additive, the additive is selected from an aprotic organic solvent with a carbon number lower than 10 and a relative dielectric constant higher than 3.6; the mass content of the lithium salt is 30%˜90%, and the mass content of the additive is 0.01%˜2%, based on the total mass of the solid electrolyte being 100%. Further provided is a polymer lithium ion battery comprising the solid electrolyte. According to the solid electrolyte of the disclosure, a trace amount of small molecule aprotic organic solvent with high dielectric constant is introduced as an additive, which can inhibit crystallization of the solid electrolyte, promote transmission of lithium ions in the electrolyte, and improve the ionic conductivity of the solid electrolyte at room temperature.