Abstract: As an important mechanical property index for materials,plane-strain fracture toughness KIC characterizing a force against material fracture,is applied in engineering design for fracture restraining.In this paper,with a set of five pieces standard compact tension specimens,plane strain fracture toughness test of TC4ELI alloy was performed and the results manifested that for the five specimens,three of them had effective test values and the other two had only qualification values.Limited conditions of plane strain fracture toughness by a test and its engineering application were argued,which would provide reference for TC4ELI alloy to be used practically.