Abstract: In order to increase the distribution of diamond particles and the thermal conductivity of polyacrylonitrile(PAN) copolymers, the diamond/PAN hybrid composite fibers were obtained via electrospinning using PAN and different sized diamonds as raw materials. The effects of different contents and various sizes of diamond on the morphology and thermal properties of diamond/PAN composite fibers were studied with changing the mass fraction of diamond addition. The results show that electrospinning can give the ability to deliver microdiamonds in the form of well-dispersed particles into the polymer matrix, and the stability and continuity of the spinning are greatly affected by the particle size of the diamonds. The size of diamond of 0.5-1 μm can be effectively coated in the diamond/PAN fiber, and the thermal conductivity of diamond/PAN fibers reaches 1.923 W/(m·K) when the actual mass fraction of diamond is 38.5wt%. However, when the size of diamond particles is greater than 1-2 μm, the stability of the spinning is poor. As a result, it will lead to the diamond being little or not even appearing in the diamond/PAN fibers.