The cross-sectional images of turbulent premixed flames of homogeneous fuel-air mixture in an engine cylinder were obtained by a laser tomography, and the fractal characteristics were investigated. It was observed that in an engine cylinder under high pressure condition, the turbulent flame was a smaller and more complicated structure, comparing with that under the lower pressure condition in a closed combustion chamber. The fractal dimension increases with the increase of the turbulence intensity and mixture density. The fractal dimension is expressed as a function of the increase ratio of mixture density and the ratio of turbulence intensity to laminar burning velocity. The inner cutoff scale of turbulent flames is expressed as a function of Karlovitz number.