Abstract: The measurement accuracy of elastic modulus of metal materials is affected by many experimental factors. In this paper, 7N21 aluminum alloy was processed into a round bar sample, and its elastic modulus was measured by static tensile test method. The influence of control mode, the use of extensometer and pretension on the measurement of elastic modulus was analyzed. The results show that the measurement accuracy of elastic modulus is less affected by the control mode and specimen pretension, which is mainly determined by the selection and use of extensometer. Using a single extensometer to measure the elastic modulus of the same sample in multiple directions and take the average value can effectively eliminate the influence of eccentric tension, and can improve the accuracy and stability of the measurement results.