In this work, effect of active layer thickness on the performance of a-IGZO based TFT has been studied by using ATLAS 2D device simulator of SILVACO TCAD software. Here, the effect of channel thickness on electrical performance of the device was studied. High mobility (> 51cm2V-1s-1) was observed for all TFTs. Threshold voltage shows an incremental nature with channel thickness. Subthreshold value and current ratio show deterioration with increase in channel thickness.