Single-screw extruders together with a painstakingly self-made dynamic mixer were applied to mix carbon black (CB) in polymeric matrix. Moreover, the master batch dilution technique was also used. The mixing state of CB was investigated by direct methods including transmission electron microscopy (TEM), scanning electron microscopy (SEM), and optical microscopy (OM). The image analysis software, Image J, was first introduced to analyze the mixing state of CB. By virtue of Image J, the average size, surface density, and area distribution of particles were automatically created. On the basis of TEM results, quantitative evaluation parameters such as Morisita’s index (I), skewness (β), and the Lacey index (M) were employed. The results reveal that CB was well dispersed and uniformly distributed in films. Besides, the area distribution abides by a lognormal equation fitted by origin. In SEM analysis, the area distribution conforms to exponent decay strictly as well as that in OM results. Furthermore, the dispersion index (D) was used to characterize the mixing state of CB. The results imply that CB tends to aggregate with increasing CB loading. Combining the methods mentioned above is favorable to quantitatively characterize the mixing state of CB, in that they can become references between one another.