The turbulent passive scalar fluxes were studied by separately considering the contributions of small-eddy motions and large-eddy ones.Explicit algebraic approximation was achieved for both small-eddy and large-eddy scalar fluxes.Especially, the large-eddy scalar flux was modelled with complex diffusivity.The singular difficulties in usual algebraic scalar models, do not occur any more in this model.In addition, this new model provides a new way to reasonably describe the negative transport phenomena appearing in asymmetric turbulent flows.