The 26th General Conference on Weights and Measures (CGPM) approved the redefinition of the International System of Units (SI) using fundamental constants. The temperature unit “Kelvin (K)” will be redefined using Boltzmann constant (k). Accurate measurement of Boltzmann constant is the key to redefining Kelvin and reproducing thermodynamic temperature. In this paper, four kinds of primary thermometers used for measuring Boltzmann constant are introduced in detail, namely acoustic gas thermometery (AGT), dielectric-constant gas thermometery (DCGT), Johnson noise thermometery (JNT) and Doppler broadening thermometery (DBT). The working principle, main parameters and practical application of the four primary thermometers are expounded, and their contributions to the revision of Boltzmann constant value is explained. Finally, the future development direction of the primary temperature measurement method is summarized and prospected, which provides research support for the reproduction and transfer of thermodynamic temperature.