An etching method of etching apparatus is disclosed. The etching apparatus performs an etching process on a material to be processed which includes a material layer and a mask layer formed on the material layer. The etching method includes the following steps. The mask layer is etched. A light intensity at a specific wavelength for light generated is detected when the etching process is performed on the mask layer to be processed and an end point detection signal is generated. An etching completion time of the mask layer to be etched is determined according to the end point detection signal. A thickness of the mask layer to be etched is calculated according to the etching completion time. An etching time of the material layer is adjusted according to the thickness of the mask layer to be etched. The material layer is etched after adjusting the etching time.