Abstract: Using fractal theory as tool, coupling with inner pore structure of semi-coke by mercury intrusion method, the fractal characteristics of pore structure were studied. Through determining the fractal dimension of pore volume quantitatively, the change of fractal dimension of pore volume with different coking temperatures and different spatial positions during pyrolysis was investigated. The results show that there is no relationship between the fractal dimension and the pore structure with pore diameter >5μm. However, the pores with diameter of 20nm～5μm can be properly characterized by the fractal theory, and a fractal dimension range of 2.45～2.83 is obtained in this work. The fractal dimension of pore volume under identical spatial position is high at low temperature, then decreases and increases and finally decreases with the increasing temperature. But a small variation of the fractal dimension, less than 0.15, is observed under identical spatial position. It shows that the effect of coking temperature on the fractal dimension is not remarkable. Additionally, the fractal dimension of pore volume at the center and brim position of coke cake is greater than that of the middle position under identical coking temperature. It indicates that the pore structure at the center and brim of coke cake is more complex than that of the middle poison.