Fracture toughness is a critical parameter in both the study of rock fracture propagation within linear elastic fracture mechanics and geotechnical engineering. It plays an indispensable role in ensuring the safety and efficiency of geotechnical construction projects. Prior to commencing construction, the mechanical properties of the rock at the construction site, including fracture toughness, are analyzed and tested. It is widely recognized by experts that rock fracture tip stress exhibits a degree of singularity, making the simultaneous calculation of T stress and rock stress intensity factor a challenging task in fracture toughness testing. Existing research highlights the significant influence of T stress on rock fracture toughness. If we can establish a linear relationship between rock fracture toughness and T stress, it could simplify the complexity of fracture toughness calculations for rock, thereby facilitating geotechnical engineering. However, currently, there is a noticeable dearth of research exploring the relationship between rock fracture toughness and T stress. In the realm of domestic research, investigations in this area began relatively recently, and the associated theoretical foundations are still in their infancy. Although there has been a growing emphasis on the mechanical properties of rock in recent years, with scholars and experts conducting extensive research on aspects such as compressive properties and hardness, there is a lack of a comprehensive theoretical framework that addresses the influence of T stress on rock fracture toughness. Consequently, this study aims to fill this critical gap, providing a solid foundation to enhance and optimize methods for calculating rock fracture toughness.