Abstract: In this paper, the linear thermal expansion coefficient of electrolytic though pitch copper (Cu-ETP) is measured high-precision and in situ by multi-modes microwave resonance method in the temperature range from 4.3 K to 299 K. Two experimental measurement schemes, cooling method (5 K-299 K) and temperature control method (4.3 K-26 K), are employed for different temperature ranges. For cooling method, the standard uncertainty of linear thermal expansion coefficient is 2.2× 10-7 K-1 and the repeatability is the main source of uncertainty. As for controlling method, the standard uncertainty of linear thermal expansion is 2.9 × 10-9 K-1 and the two main sources are microwave modes consistency and repeatability. Due to higher stability of temperature control and lower microwave measurement noise, the results determined by temperature control method are more accurate. Finally, equations for linear thermal expansion coefficient of Cu-ETP are further developed to realize high-precision correlation between experimental data and temperature.