To analyze the effects of applicator types and emitting characters on laser-induced interstitial thermotherapy (LITT), based on an optical-thermal mathematical model considering the dynamic changes of physical properties during laser heating, the sizes and shapes of thermal damage regions for bare fiber tips and diffuse applicators were numerically calculated and compared. The effect of the un-uniform emitting radiation of practical diffuse applicator on the thermal damage region was also analyzed numerically. The numerical results showed that the thermal damage region with diffuse applicator was much larger than that with bare fiber for long time heating. The thermal damage region was not spherical symmetry about the fiber tip for bare fibers while approximately ellipsoidal for diffuse applicators. The numerical results also showed that the thermal damage region was not sensitive to the un-uniform emitting radiation of practical diffuse applicators. Applicator types and emitting characters significantly affected the thermal damage regions during laser-induced interstitial thermotherapy.