The size of exposed fractures in rock masses are critical indicators for evaluating rock mass stability. This study focuses on rock masses with exposed fractures, analyzing the impact of fracture size on the rock mass temperature field through laboratory experiments. Criteria for defining fracture boundaries are established, and a formula is derived based on one-dimensional heat transfer theory, using rock mass temperature field, time, and fracture depth as variables. The applicability of the fracture depth calculation formula is determined through error analysis. The results indicate that after heating the surface of exposed fractures using radiative thermal excitation, a significant correlation exists between the fracture width, depth, and the minimum temperature of the fracture area in infrared images. Depth is the primary influencing factor, with the influence coefficient of fracture width being less than 0.1 times that of depth. The identification error for the exposed fracture area can be controlled within approximately 10%. As fracture width increases, the identification error gradually decreases, with the minimum error as low as 0.2%. The error in theoretical formula-based fracture depth calculation decreases with prolonged heating time. Heating for 30 minutes ensures a calculation error of less than 20% for fractures with depths within 40 mm. Extending the heating time to 60 minutes reduces the calculation error for 50 mm depth fractures from 24.8% to 6.8%. In summary, using infrared thermal imaging technology to detect the exposed area and depth of fractures shows high feasibility and holds significant application value for rock mass engineering where contact measurements are challenging.