Abstract: The double-K fracture criterion describes initiation, stable propagation and unstable propagation of cracks in concrete structures. The corresponding double-K fracture parameters (K_ICⁱⁿⁱ and K_IC^un) introduced in the criterion can be determined using a simple experimental method combining with an analytical evaluation based on the cohesive force on the fictitious crack zone. The results show that the initial fracture toughness K_ICⁱⁿⁱ depends on the softening traction-separation law used in the calculation. With regard to the convenient bilinear softening traction-separation law, the parameters σ_s、w_s、w₀ will influence on the softening traction-separation law. Comparing with the results of wedge splitting tests which were conducted recently, the parameters in the softening traction-separation law can be determined to evaluate the double-K fracture parameters.