Modified CFs were firstly used as reinforcement phases of composites made by selective laser sintering (SLS). The interfacial adhesion between fillers and matrix in SLS were firstly discussed. The oxygenic groups on the surface of CFs were thermally decomposed during the sintering process. Treating CFs at 400 °C after HNO3 modification can decrease the porosity of sintered composites. The practical application problems of modified CF/PA12 composite powder in SLS were resolved.