Randomly copolymerized polyimide(co-PI) fibres were prepared from pyromellitic dianhydride (PMDA), 4,4'-oxydianiline (ODA), and p-phenylenediamine (p-PDA) by two-step wet spinning process. Co-PI fibres were carbonised at 1400 degrees C under a pure N-2 atmosphere for preparing carbon fibre and then graphitised at 2800 degrees C under a pure Ar atmosphere for preparing graphite fibre. The influence of ODA/p-PDA molar ratios on the molecular weight and molecular weight distribution, chemical structure, morphology, thermal stability and carbonisation yield of co-PI fibre were carefully discussed. Co-PI fibres with 50% ODA content (POP-50%) has the highest thermal stability and the lowest heat release during the carbonisation process. The relationship of structure and property between co-PI fibres and co-PI based graphite fibres were analysed by XRD, Raman and thermal conductivity test. Co-PI based graphite fibres showed an increased graphitisation degree and crystal lattice size L-a(110) with the proper amount of ODA adding. The thermal conductivity of co-PI based graphite fibres showed a close relationship with L-a(110). POP-20% reaches a maximum L-a(110) of 170 nm and the highest thermal conductivity of 305.2W m(-1) K-1 which is 35.2% higher than that of POP-0%.