((-1 + 3 r) \[Theta] +
t (3 - 2 \[Theta] +
r (-5 + 2 \[Theta]))/(4 (-1 + r) \[Theta]^2 + (1 + r) t^3 (8 -
5 \[Theta] + r (-8 + 3 \[Theta])) +
t \[Theta] (16 - 5 \[Theta] - 5 r^2 \[Theta] +
2 r (-8 + 3 \[Theta])) +
t^2 (-16 + 5 \[Theta] +
r^2 (13 - 3 \[Theta]) \[Theta] + \[Theta]^2 +
2 r (8 - 7 \[Theta] + 3 \[Theta]^2))))>0, 各变量取值范围为：{t, 0,
1}], {\[Theta], 0, 1}, {r, 0, 1}

ClearAll["Global`*"]
\[CapitalOmega] =
ImplicitRegion[(-1 + 3 r) \[Theta] + (
t (3 - 2 \[Theta] + r (-5 + 2 \[Theta])))/(
4 (-1 + r) \[Theta]^2 + (1 + r) t^3 (8 - 5 \[Theta] +
r (-8 + 3 \[Theta])) +
t \[Theta] (16 - 5 \[Theta] - 5 r^2 \[Theta] +
2 r (-8 + 3 \[Theta])) +
t^2 (-16 + 5 \[Theta] +
r^2 (13 - 3 \[Theta]) \[Theta] + \[Theta]^2 +
2 r (8 - 7 \[Theta] + 3 \[Theta]^2))) > 0 && 0 < t < 1 &&
0 < \[Theta] < 1 && 0 < r < 1, {r, t, \[Theta]}]
RegionPlot3D[\[CapitalOmega], PlotPoints -> 150]