  Motivated by the finding of nearly isotropic superconductivity in
$\mathrm{(Ba,K)Fe_2As_2}$, we use renormalized mean field theory to
investigated the $t$-$J$ model on three-dimensional simple cubic lattice. A
tunable anisotropic parameter is introduced to dictate the coupling on $z$
direction. The symmetry of the superconducting order is studied in detail.
Calculation shows that for the isotropic case, pairing parameters on the three
perpendicular directions have ${2/3}\pi$ phase shift to each other. However,
when the interaction on $z$ direction is suppressed, the corresponding
amplitude of the pairing parameter decreases rapidly, furthermore,
two-dimensional d-wave state pairing is favored when the anisotropic rate less
than 0.75.
