Based on weight integration to obtain a closed solution of cohesive crack problem, a new method is proposed to determine the tensile-strain softening curve (TSC) for quasi-brittle materials. The key technique is to determine the weight function by superposition of the solution with different fictitious crack lengths to satisfy a given crack opening displacement within cohesive crack surfaces. As an example, a central crack problem under uniform tension with given crack opening displacement in the fracture process zone (FPZ) was analyzed, the corresponding TSC was determined, and then the solution for stress and displacement field was obtained.