For the purpose of explore the effects of chopped carbon fibers (CFs) on the microscopic characteristics of the internal pore structure of concrete, chopped carbon fibers reinforced concrete (CFC) specimens with volume content of 0%, 0.1%, 0.2%, 0.3% and 0.5% of CFs were prepared. The internal pore structure characteristics of each group of specimens were analyzed by means of mercury intrusion porosimetry (MIP), and the fractal law of pore size was further discussed by introducing fractal theory. The results show that adding an appropriate amount of CFs can effectively reduce the total porosity and average pore size of concrete, and the improvement effect reaches the best when the content of CFs is 0.1%. The inner pore size shows remarkable fractal characteristics, and the fitting correlation coefficient R2 of ln(Wn/r2n) and ln Qn of each group specimens of concrete is more than 0.996, which means the slopes can be used as pore surface fractal dimension (Dp). The Dp decreases firstly and then increases with the increase of CFs content, and the larger the Dp is, the larger the average pore size is, which further verifies the improvement law of CFs on the internal structure of concrete.