Abstract: The influence of process parameters in fused deposition modeling and annealing heat treatment on the microfiber orientation of short carbon fiber-reinforced nylon 6 was investigated in the study, as well as the differences in fiber orientation after fused deposition modeling for this material with varying carbon fiber slenderness ratio. Microscopic observations were conducted on single-layer-single-fiber samples, and Image J software was used to measure the planar fiber orientation angles. Histograms of planar fiber orientation under different process parameters were obtained and fitted with normal curves for comparative analysis. The experimental results indicate that with increasing printing speed, the number of fibers oriented in the printing direction first rises and then falls, reaching a peak at V=40 mm/s, with a standard deviation σ of 11.14 and a frequency peak of 0.42. Additionally, the tensile modulus follows a similar trend, and Pearson correlation analysis reveals a strong correlation between the two. Fiber orientation consistency does not improve with an increase in carbon fiber slenderness ratio, but is related to the retained slenderness ratio in the specimen. At different annealing temperatures, the impact on fiber orientation is more pronounced when the annealing temperature is between the glass transition temperature and the crystallization temperature, with the optimal effect achieved at 150℃ with a standard deviation of 6.39 and peak frequency of 0.54.