The evolution of pore fractal dimensions for three Chinese chars was investigated. The pores of porous chars can be classified into macro-, micro- and transition-pores based on their fractal dimensions. The radius ranges of the macro-, micro- and transition-pores may be different for various chars. For different conversions in the char combustion process, the fractal dimensions of the micro-pores for different chars are almost the same and the fractal dimensions of macro-pores for the same kind of chars are roughly unchanged. The effects of fractal structure on combustion rate are also discussed.