A method and system for describing image region based on color histogram is provided. The method for describing an image region based on color histogram comprising: a color quantization step for quantizing said image region into a quantized color region, wherein a specific color range and colors outside the specific color range are differently treated in the quantizing; a color histogram calculation step for computing one or more color histograms according to said quantized color region; and a histogram assembling step for generating a unique vector by using said one or more color histograms.