With the continuous development of society, people's needs for food quality testing and national security, which are closely related to daily life, are becoming more and more urgent. The novel ambient pressure ionization technology has advantages of time saving, high sensitivity, real-time online, etc. It has been widely used in food detection, drug analysis, explosives screening, chemical reaction monitoring, and living imaging. This paper describes the basic principles and methods of ionization from the traditional atmospheric pressure ionization technology. On this basis, the direct ionization technology, direct desorption/ionization technology, assisted desorption/ionization technology, and the differences between different ionization techniques are introduced. Finally, the development trends of ambient pressure ionization technology are also discussed.