With the advancement of science and technology, effectively addressing the issue of heat dissipation in electronic equipment has become a key research topic. Polymers have attracted attention due to their low price, excellent flexibility, and lightweight characteristics, but thermal conductivity has a limitation. In this work, aiming for all-polymer composites with lightweight and high thermal conductivity, poly(p-phenylene benzobisoxazole) (PBO) fibers were used to construct a long-range ordered heat transfer path in the organosilicon matrix, and an all-organic composite material with a low density of 1.24 g cm-3 and thermal conductivity of 18.44 W/ (m K) was produced. At the same time, the composite material was applied to the cooling performance test of LED lamps, which was 4.8 °C lower than advanced commercial thermal conductive materials, demonstrating its potential in the field of thermal management materials.