A black and white stretching system and method for improving contrast of a picture is disclosed. The system includes a histogram distribution calculation unit for calculating a histogram distribution of an input signal of a specified unit, a mean calculation unit for calculating a mean level of the input image signal, a slope calculation unit for calculating black and white stretching slopes in association with the mean level, a ratio calculation unit for calculating a ratio of a picture change based on the histogram distribution of the present input image signal and the previous input image signal, a filtering unit for adjusting the black and white stretching slopes corresponding to the ratio of the picture change, and a stretching unit for stretching the input image signal by mapping the adjusted black and white stretching slopes and the input image signal.