The teaching method of obtaining Boltzmann constant by measuring the thermal noise of a resistor with a lock-in amplifier is easy for students to understand in physics, and its smooth implementation requires technical support of high precision measurement and students’ clear understandings of the measurement principle and the meanings of instrument parameters of the lock-in amplifier. To meet the peculiarity and the requirements of physics specialty, especially that of precision measurement physics, it is tried to avoid as much as possible involving in knowledge of electronics, but focus on mathematical description of noise measurement with a lock-in amplifier, including the derivations of thermal noise of a resistor, the noise processing process of a lock-in amplifier, and the equivalent noise bandwidth. The experimental design of Boltzmann constant measurement is optimized based on error analysis. Finally, the preliminary teaching practice is briefly introduced.