In this paper, the principle and application of plasma are briefly described, and in particular, the principle and practical application for plasma generated in liquid are introduced. Also, the research results of water treatment, synthesis of metal nanoparticle, synthesis of visible light-responsive photocatalyst, synthesis of energy material, and hydrogen gas production, which were tested using liquid phase plasma, are introduced. Various water pollutants were treated and hydrogen gas was produced using the strong chemical oxidizing species and ultraviolet rays in the plasma field generated in the reactant aqueous solution during the liquid phase plasma (LPP) process. The effects of plasma discharge conditions, dissolved oxygen concentration, pH value, photocatalytic behavior, as well as the properties of organic solutions on the LPP reaction were investigated experimentally and reported. Based on these previous studies, metal nanoparticles were synthesized using hydrogen atom radicals as well as the numerous electrons in the plasma field generated during the LPP process. Additionally, these studies indicate that visible light-responsive photocatalysts can be obtained when metal nanoparticles are precipitated in TiO2. They also provide evidence that metal nanoparticles can be precipitated in various carbon materials for application as electrodes in secondary batteries and supercapacitors. Therefore, the LPP process has been successfully applied in various fields given that it can be easily and conveniently used, and presently it is being applied in several new fields and many possibilities for its future application are expected.