Abstract: Long PAN-based carbon fiber was surface-modified by pyrophosphate copper plating with self-made equipment. The influences of bath composition, current density, plating temperature and pH value of bath on quality of coating were systematically analyzed to optimize the continuous copper electroplating process parameters, and C/Cu composite fiber with better properties was prepared. The results indicate that the problem of black core and agglomeration were well solved by electroplating in a bath with content (mole fraction) ratio 7.0 of P₂O₇^4- to Cu²⁺ and 25 g·L^-1 ammonium citrate as the additive under the conditions of current density of 2.0-2.5 A·dm^-2, bath temperature of 40℃, and bath's pH of 8.2-8.8. The obtained coating is complete, uniform and compact, it also owns high bonding strength, and the C/Cu composite fiber obtains significantly enhanced conductivity.