In this work, a difference finite element (DFE) method is proposed for solving 3D steady convection-diffusion equations that can maximize good applicability and efficiency of both FDM and FEM. The essence of this method lies in employing the centered difference discretization in the $z$-direction and the FE discretization based  on the $P_1$ conforming elements in the $(x,y)$ plane.  This allows us to solve PDEs on complex   cylindrical domains at lower computational costs compared to applying the 3D FEM.  We derive the stability estimates for the DFE solution and establish the explicit dependence of $H_1$ error bounds on the diffusivity, convection field modulus, and mesh size. Moreover, a compact DFE method is presented for the above problems. Finally, we provide numerical examples to verify the theoretical predictions and showcase the accuracy of the proposed method.