The present invention relates to a fracture elongation rate, and discloses a testing method for the fracture elongation rate with an original gauge length mantissa being 5. the method comprises following steps: before testing, requiring to select a suitable testing tool, and to select a same person to perform test, to avoid a situation where test adjustments do not agree; in order to perform fracture growth rate test, requiring to prepare a gauge punching machine, a vernier caliper and a operating bench for testing, and when ready, fixing the gauge punch machine and the vernier caliper on theoperating bench. Testing method for fracture elongation rate with the original gauge length mantissa being 5 measures the original gauge length by using three different methods. If the original gaugelength mantissa is an integer, conventional calculation can be performed; If the original gauge length mantissa is 5, according to fluctuation of numerical values, one of three measuring methods can be used, so that the fracture elongation rate of brittle strip materials can be detected quickly and effectively.