Quasi-CW laser damage behaviors of indium tin oxide (ITO) single-layer and polyimide (PI) on ITO bi-layer were investigated. The ITO single-layer with thickness of 25nm was deposited on fused silica substrate by magnetron sputtering, and the PI/ITO bi-layer was prepared by spin coating 80nm PI film on the 25nm ITO single-layer. Single-shot, with radiation time of 120 seconds, laser induced damage threshold (LIDT) of the samples were determined according to ISO 21254. The damage morphologies were mapped by optical profiler. It showed interesting phenomena that the PI top layer increased LIDT of the sample. The typical damage morphologies were blisters, and the height of the blisters increased as the laser power density increases. The formation and evolution of the blisters were analyzed.