  Let $T=\left(
  \begin{array}{cc}
  R & M
  0 & S
  \end{array}
  \right) $ be a triangular matrix ring with $R$ and $S$ rings and $_RM_S$ an
$R$-$S$-bimodule. We describe Gorenstein projective modules over $T$. In
particular, we refine a result of Enochs, Cort\'{e}s-Izurdiaga and Torrecillas
[Gorenstein conditions over triangular matrix rings, J. Pure Appl. Algebra 218
(2014), no. 8, 1544-1554]. Also, we consider when the recollement of
$\mathbb{D}^b(T{\text-} Mod)$ restricts to a recollement of its subcategory
$\mathbb{D}^b(T{\text-} Mod)_{fgp}$ consisting of complexes with finite
Gorenstein projective dimension. As applications, we obtain recollements of the
stable category $\underline{T{\text-} GProj}$ and recollements of the
Gorenstein defect category $\mathbb{D}_{def}(T{\text-} Mod)$.
