The fluctuation characteristics of slug frequency was investigated on the basis of fractal theory for air/water slug flow in a downwardly inclined pipe.The results showed that the fluctuations was some chaotic vibrations which was sensitive to initial conditions.The results also indicated that the fluctuation obeyed fractal statistics law

and kept permanent characteristics.By carrying out an analysis about the fluctuation of slug frequency at two superficial liquid velocities

it was found that long-range dependency of slug frequency fluctuation were weakened with the increase of mixture velocity and the fluctuation was more sensitive to initial conditions when superficial liquid velocity was low

and the sensitivity of slug frequency to initial conditions was less affected by superficial mixture velocity when angle of pipe inclination became larger

but the angle of pipe inclination had less influence on the chaos of slug frequency on condition that superficial liquid velocity and superficial mixture velocity were large.