Carbon Fiber Reinforced Thermoplastic Composites (CFRT) are recognized as a new generation of advanced strategic materials due to their excellent mechanical properties and high recycling rate. However, in the milling process, affected by the coupling of force and thermal, the heat-sensitive resin in CFRP is easily softened and deformed, leading to difficulties in achieving high-quality material removal. Especially in the complex and long-period surface milling process, the processed surface has a complex and irregular microscopic topography, hard to be accurately characterized by traditional roughness measurement methods. To evaluate the surface quality of CFRT profile after milling more precisely, in this paper, the influence of cutting parameters on fractal dimension is systematically analyzed by solving the image gray surface based on the fractal dimension algorithm and calculating the fractal dimension of the surface after milling via the variational method. The experimental results show that the surface fractal dimension of thermoplastic composites processed by PCD milling cutter is between 2.46 and 2.52, and the sensitivity ranking of fractal dimension to cutting parameters is: v f<A e<A p.