With the development of science and technology, new flow-measuring instruments have been rapidly promoted and applied. According to their principles, they can be divided into differential pressure flowmeters, volumetric flowmeters, turbine flowmeters, electromagnetic flowmeters, float flowmeters, vortex flowmeters, ultrasonic flowmeters, and mass flowmeters. Flowmeters with different principles correspond to different media and working conditions. In practice, various factors should be considered in a unified way.