Abstract: The one-side electronic extensometer fastened on only one side of tensile specimen cannot eliminate the effect of bend of eccentric tension. The results of measurement of such electronic extensometer are instable and then more errors may be included. The first writer of this paper designs the two-side electronic extensometer, which also has two edges but it can be fastened on two symmetric sides of the tensile specimen. As a result, it can eliminate the effect of bend of eccentric tension and measures the pure tensile elongation of specimen. In this paper the error in application with the one-side electronic extensometer is revealed, and a simple figure of the two-side electronic extensometer is provided and a proof of measurement principle of the two-side electronic extensometer is given with mechanics mechanism.