Cytology is a branch of biology, which studies the morphology, structure and function of cells and their growth, differentiation and evolution. The physiological functions of organisms and all life phenomena are expressed by cells as the basic unit. Therefore, cytology is very important for understanding the inheritance, development and physiological functions of organisms, as well as pathology, pharmacology and agricultural breeding as the basis of medical treatment. Any biological phenomenon comes from the function of cells, so all fields of biology are related to cytology. Cytology, as an independent subject, began with the establishment of cell theory of M.J.Schleiden( 1838+0838) and T.Schwann (1839). With the development of biological tissue culture, microdissection, electron microscope, ultraviolet microscope, phase contrast microscope, ultracentrifugation and freeze-drying methods, the theories of cell physiological functions such as cell structure, mitosis, intracellular osmotic pressure and cell membrane permeability have been developed and confirmed. After entering the 20th century, more and more attention has been paid to the application of cytology.