  The structure of heavy hyperhydrogen $^6_{\Lambda}$H is studied within the
framework of a $tnn\Lambda$ four-body cluster model. Interactions among the
constituent subunits are determined so as to reproduce reasonably well the
observed low-energy properties of the $tn, t\Lambda$ and $tnn$ subsystems. As
long as we reproduce the energy and width of $^5$H within the error bar, the
ground state of $^6_{\Lambda}$H is obtained as a resonant state.
