An octet-truss structure is considered as one of promising candidates for modern heat exchanger structures due to its light weight with stress supporting structure and high thermal performance as a multifunctional heat exchanger. A design strategy has been established to control the anisotropy of its effective thermal conductivity tensor by deforming the structure according to its specific heat transfer application. The solution surface of flat triangle was constructed in the space with three coordinate axes being the principal components of the effective thermal conductivity, using the analytical expressions derived for metal frame structures of low solidity. The design parameters of two structural angles can readily be found from this analytical solution surface with equal angle lines to transfer heat in a particular direction, or to block heat in any other direction. Full three-dimensional (3D) numerical computations were also conducted to verify the validity of the present analytical strategy.