As the core equipment of the power system, large generators are developing in the direction of small size, large capacity and high voltage level. This trend poses a double challenge to the main insulating materials for large generators: they must meet the requirements for reliable insulation under high voltage operating conditions in power systems, and they must also have excellent thermal conductivity. This study fabricates mica tape composites using 5 μm hexagonal boron nitride (h-BN) as filler, systematically evaluating how different h-BN loadings affect both thermal conduction and electrical insulation characteristics of the resulting composite material. The experimental results show that the thermal conductivity of h-BN/mica tape is positively correlated with the h-BN content. At 20 wt.% h-BN content, the h-BN/mica tape achieved its peak thermal conductivity of 0.395 W/(m·K), representing a 98.49% increase compared to pure mica tape (0.2 W/(m·K)). Furthermore, the breakdown field strength of h-BN/mica ribbons decreases gradually with higher h-BN content. However, all measured values consistently exceed 28 kV/mm. Modified mica tape with excellent mechanical properties. The high thermal conductivity mica tapes developed in this study show promising potential for use in main insulation systems of large electrical machines.