Abstract: The melt flow properties and injection molding process of carbon fiber reinforced nylon 66 (CF/PA66) composites granules with different fiber mass fraction were analyzed and simulated respectively by capillary rheometer and homemade small molds. The parameters of CF/PA66 injection molding process were quickly obtained. The results show that the melt of CF/PA66 composites belongs to the power-law fluid, and the melt viscosity changes significantly with temperature, pressure and the carbon fiber mass fraction, the melt rheological properties change from pseudo-plastic area into Newton area while the temperature and pressure go up to the critical value. With the increase of the carbon fiber mass fraction, the suitable molding temperature of CF/PA66 improves, that of PA66, PA66 with 10wt% and 20wt% CF in our experiments are 278-285℃, 280-287℃ and 290-298℃, respectively. By means of Bagley pressure correction to the melt, the smallest injection pressure of three granules suitable for forming are 24.3 MPa, 29.4 MPa, 35.1 MPa, respectively. These parameters from rheometer simulation are applied to injection molding process, it is found that the tensile strength of samples prepared by rheometer is quite close to the samples by injection molding, which will further prove that the capillary rheometer simulation of CF/PA66 injection molding process is feasible and effective, and provid the theory basis to determine the injection molding.