Abstract: In this paper the parabolic approximation method is used to study combined propngations of wave - current over a slowly varying and frictional topography. A governing equation included the friction effects is firstly given by the author. A simplified form is presented after the examination of wave - current conservation equation and the bed friction model given by Yoo and O'connor, Calculation examples revealed that the computational method presented in this paper can be used for calculation of wave elements in practical engineering design with large water area.