A method for filtering noise in an image filters noise pixels in a discrepant block between a current image and a background image firstly, and further filter each small block whose area is less than a preset value from the discrepant block. The method further calculates a total area of each big block whose area is greater than or equal to the preset value from the discrepant block, and adds the current image to a background list of the current image if the total area is less than another preset value.