Abstract: A study of the interfacial behavior and internal thermal stress distribution in fiber-reinforced composites is essential to assess their performance and reliability. CNT/carbon fiber (CF) hybrid fibers were constructed using electrophoretic deposition. The interfacial properties of CF/epoxy and CNT/CF/epoxy composites were statistically investigated and compared using in-situ thermal Raman mapping by dispersing CNTs as a Raman sensing medium (CNT_R) in a resin. The associated local thermal stress changes can be simulated by capturing the G' band position distribution of CNT_R in the epoxy at different temperatures. It was found that the G' band shifted to lower positions with increasing temperature, reaching a maximum difference of 2.43 cm⁻¹ at 100 °C. The interfacial bonding between CNT/CF and the matrix and the stress distribution and changes during heat treatment (20–100 °C) were investigated in detail. This work is important for studying thermal stress in fiber-reinforced composites by in-situ thermal Raman mapping technology.