With the modification of plasma spray parameters, porosity ratio of top coat can control along the cross-section. This improves the thermal cycle resistance and decrease the thermal conductivity. Plasma sprayed ZrO2/8 wt.–% Y2O3–NiCrAlY TBC systems which have different porosity (%8-12) and range of 250-350µm thicknesses of top coats, during thermal cycling tests with different hold times at 1350 °C have been performed. The main failure modes: delamination cracking, TGO growth rate and phase transformation are strongly dependent on the hold temperature and time. The correlation between TBC thermal cycle lifetimes and duration of high temperature hold time per cycle is shown and discussed with depending on thickness and porosity ratio.