Abstract: The evolution of the definition of kilogram,the basic unit of SI,was discussed.The specific causes that drive the rapid realization of quantization of mass unit was clarified with the corresponding impact on mass metrology and electrical metrology.The internal logic of quantization of mass unit based on Avogadro constant and Planck constant was analyzed.The specific principle of establishing a relation between macroscopic mass and Planck constant by watt balance was discussed.The development and relative standard uncertainties of the measurement of watt balance in six institutions such as NPL,NIST and NIM was introduced.The data show that China has entered the international advanced level in the field of mass quantum metrology.

Key words: Mass quantum metrology, International prototype, Watt balance, Planck constant