A 3D eddy current mathematical model of fixed clamp for large cross-section power cable is proposed in this paper. The effect of the current of cable core, the conductivity of fixed clamp material and the thickness of fixed clamp on the eddy current losses of fixed clamp is studied adopting FEM under the consideration of initial and boundary conditions. The calculation results show that the eddy current losses of cable cleat are increased with the increase of current, conductivity and thickness. When the current is large, the eddy current loss of fixed clamp changes rapidly. When the conductivity is large, however the eddy current losses of fixed clamp change to flatten. And, the change of the eddy current losses of fixed clamp with the thickness is approximately linear relationship. This paper also put forward to choose stainless steel as the power cable cleat material can effectively reduce the eddy current losses produced by cable cleat.