The extent of thermal damage in the glass fiber reinforced composite blade is highly dependent on the severity of the lightning current, which also determines the mechanism of lightning-strike-induced heat transfer in the composite. Lightning attachment at the electrically non-conductive glass fiber reinforced polymer (GFRP) composite surface may come as a direct heat injection. However, if the electric field at the attachment point is sufficient, the breakdown of the GFRP composite occurs. In this case, in addition to the direct heat injection at the surface, Joule heating will be produced in the newly conductive glass fiber reinforced composite. Therefore, it is crucial to determine whether dielectric breakdown can occur prior to formulating the problem. In this work, lightning-strike induced heat transfer in a GFRP composite wind turbine blade is analyzed. First, several models are employed to estimate the electric field in the vicinity of a wind turbine blade to determine if dielectric breakdown occurs. The wind turbine blade under consideration is the Sandia 100-meter All-glass Baseline Wind Turbine Blade (SNL 100-00). Results show that the dielectric breakdown of the composite blade is not likely to occur for a lightning stepped leader under three lightning protection levels (LPL I, LPL II and LPL III). Therefore, only the direct heat injection problem at the composite blade surface is considered, and the nonlinear transient heat transfer problem for a layered temperature-dependent GFRP composite panel is solved using finite element analysis.