Since 1963 radio astronomy successfully detected interstellar molecules, great progress has been made in the study of interstellar molecules. Especially in the last decade, many kinds of molecules have been found in interstellar space and neighboring extragalactic galaxies. By the end of 1979, more than 50 kinds of interstellar molecules had been identified, and by 2004, more than 30 kinds of1979 had been identified. Each molecule often has several or even hundreds of sources, which are distributed in various regions with different physical conditions in interstellar space, such as the center of the Milky Way, ionized hydrogen and neutral hydrogen regions, circumstellar matter, dark nebulae, supernova remnants and infrared stars. Some molecules (such as carbon monoxide) are widely distributed and can be used to study the spiral arm structure of the Milky Way and other galaxies. But some molecules can only be found in very dense nebulae. The famous Orion A nebula, located in the ionized hydrogen region, is one of the most detailed molecular sources, from which many molecules have been found. Sagittarius A and Sagittarius B2 in the center of the Milky Way are more abundant molecular sources, and almost all discovered interstellar molecules can be found here. The formation process and chemical evolution of interstellar molecules are not very clear. Some claims are that ionized atoms (molecules) collide and are formed by dust particles in gas clouds. Understanding the formation process of many molecules, especially organic molecules, and their relationship with the origin of life on earth is an important subject of interstellar chemistry, a new branch of astronomy.