Abstract: The interlayer interface was unavoidable in 3D parts additive manufactured by fused deposition modeling. Aiming at the enhancement of the interlayer interface, the poly (lactic acid) (PLA) based biocomposite filaments were formerly prepared by the ultrasonic impregnating. In the PLA based biocomposite filament, nano-hydroxyapatite (n-HA) and micron chopped carbon fiber (CF) were firmly bonded and uniformly distributed on the surface of the PLA filament, and they were reserved as reinforcement phases for interlayer interface after being fused. However, after fused deposition modeling, the distribution state of above two reinforcement phases was particularly critical, and it was closely decided by the melting fluid velocity of the nozzle outlet. The influence of three key factors of nozzle diameter, filament feeding speed and micron chopped CF content on the melting fluid velocity of the nozzle outlet was studied, with Ansys being used for fluid numerical calculations, Minitab being applied for orthogonal parameter design and signal-to-noise ratio data analysis, standard tensile samples being 3D printed for tensile performance characterization and distribution state observation of above two reinforcement phases. The results show that the optimization of experimental parameters with Minitab signal-to-noise ratio is more effective than orthogonal experimental parameter design along. Since then, when the melting temperature is 210℃, the nozzle diameter is 0.5 mm, the filament feeding speed is 14 mm·s⁻¹, and the micron chopped CF content is 7wt%, the melting fluid velocity of the nozzle outlet numerically owns the largest variance, which means the most uniform distribution of the above two reinforcement phases in the interlayer interface, and the sample experimentally obtains the strongest tensile properties.