Abstract: Let T = \left( \beginarray*20c A_1&0&0 \\ U_21&A_2&0 \\ U_31&U_32&A_3 \endarray \right) be triangular matrix ring of order 3, where A_i are rings (i = 1,2,3) and U_ij are (A_i,A_j) -bimodule (1 \leqslant j < i \leqslant 3) . We obtain equivalent condition that module over ring T is Gorenstein projective module. Suppose M = \left( \beginarray*20c M_1 \\ M_2 \\ M_3 \endarray \right)_\varphi ^M is left T -module. If U_ij(1 \leqslant j < i \leqslant 3) as left A_i -module, they have finite projective dimensions, U_32 as right A_2 -module, it is flat, and U_i1(i = 2,3) as right A_1 -module, they have finite flat dimensions, then M is Gorenstein projective left T -module if and only if M_1 is Gorenstein projective left T -module, and each i = 1,2, \varphi _i^M:U_i + 1,i \otimes _A_iM_i \to M_i + 1 is monomorphism, and \rmcoker \;\varphi _i^M is Gorenstein projective left A_i + 1 -module. At the same time, we also characterize Gorenstein projective dimensions of left T -module M.