Potassium (K) and magnesium (Mg) are important nutrients elements for plant growth and development. K, Mg and their interaction, and ion balance are focused gradually by scientists in recently years. This paper reviewed the study work on K, Mg and their interaction over the past several decades and looked forward to the research direction in the future. It discussed mainly the plants growth and development, nutrients uptakes and translocations, plants quality, physiology and biochemistry, carbon and nitrogen metabolism, active oxygen metabolism, and the potassium and magnesium cations in soil. In addition, it also discussed some prospects in the research on K, Mg and their interaction.