Relativistic plasma mode conversion‐tunneling equations at the second and third electron cyclotron harmonics are derived. A finitek∥is introduced which keeps the coupling between the O‐mode, the X‐mode and the Bernstein wave in the mode conversion problem for the first time. The solutions for these mode conversion problems without absorption are obtained, and the connection formulas between different wave branches are established. The corresponding transmission, reflection and conversion coefficients are also given. A comparison between the coupled equation and the uncoupled equations is also made.