The process of potassium uptake and utilization in plants is very complex. Recently, much work has been done on the research of mechanism of plant high K use efficiency and great positive results on plant K efficiency and its evaluation have obtained. This paper briefly summarized the concepts, differences and physiological mechanism of plant K use efficiency. The research reports on soil potassium sink, root characteristics, root exudates and microorganism, potassium translocation and relocation at both cellular and plant levels, substitution of other ions to K+, harvest index and some relative new results in the field of molecule biology has also been reviewed. Additionally some indices of K use efficiency and some related problems in using the indices are discussed as well.