High-frequency (HF) beam wave propagation in a turbulent stratified ionosphere is investigated. At oblique incidence the beam wave is refracted in the ionosphere with its amplitude and phase calculated by geometrical optics approximation. The diffraction from the bottom of the ionosphere down to the ground is taken into account by solving a parabolic equation. Under appropriate assumptions, numerical results for the two-frequency mutual coherence function and the mean field are obtained. It turns out that the random medium does have effects on the beam wave propagation. As the turbulence strength increases, the coherence bandwidth of the wave is greatly reduced. Thus the width of a pulsed wave will be broadened if it propagates in the random ionosphere.