Abstract: Soil protists are the most primitive and simple eukaryotes living in litter and soil. The evolution of protists is fast and the species are diverse. So far, there is no unified phylogenetic classification system. A wide variety of soil protists have diverse ecological functions. Protists play important roles in controlling the growth and reproduction of bacteria and its community composition, changing soil nutrients cycling, regulating plant growth and controlling pollutant transformation. This review summarized the evolutionary process, phylogenetic classification and functions, the geographical distribution and research methods of protists, the relationships among protists, soil microorganisms and plants, and the potential impact of protists on the environment. It aims to deeply understand the generation and maintenance mechanism of soil protist biodiversity, and the interactions among protists, microorganisms and plants, and develop new biological control measures for soil and vegetation diseases.