This standard specifies a method for determining the fracture toughness of plastic materials under Mode I crack opening within the framework of linear elastic fracture mechanics, used to evaluate the material's resistance to crack propagation. The core of the method involves using a universal material testing machine to load specimens with pre-existing cracks, primarily employing two typical methods: three-point bending tests and compact tension tests. By accurately measuring load and displacement, two key fracture toughness parameters—the critical energy release rate (GIC) and the critical stress intensity factor (KIC)—are calculated. This standard applies to rigid and semi-rigid thermoplastics, thermosetting plastics, and their short-fiber reinforced composites, providing authoritative testing criteria for the design selection and safety assessment of related engineering materials.