Density meter is an important instrument used to measure the mass per unit volume of a substance. It is widely used in petrochemical, food and beverage, pharmaceutical, metallurgy, material research and other fields. Due to different application scenarios and measurement objects, there are many types of density meters, which can easily confuse people when selecting. ATO will systematically classify density meters from three dimensions: usage scenarios, measurement media and working principles, and illustrate them with typical examples to help everyone quickly understand the characteristics and uses of various types of density meters.