In order to significantly extend the limit of the measurable strain range to obtain true stress-strain curves of materials using tensile testing, digital image correlation is used to measure local strains. In this study, a method to measure reliable true stress-strain curves in a wide range of strains covering the post-necking stage with reducing gage lengths has been investigated. In tensile testing, by decreasing the gage length for the strain measurements, not only accurate true strain but also reliable true stress can be obtained until sample fractures. This experimental method for accurate true stress-strain measurements is verified by comparing the experimental results and the finite element method simulated load-displacement curve, geometries, and strain distributions. The new method can be used to easily obtain the measurement of accurate and extended true stress-strain curves, which can assist in experimental and theoretical investigations of the mechanical behavior of materials. This simple method has shed new light on the measurement of the mechanical properties of materials for both experimentalists and simulation engineers, who need a wide range of true stress-strain curves.