The present invention relates to a grey level processing method for a sheet light map generated by a Fresnel lens. Firstly, a sheet light map is collected, and the grey level value of each pixel in the map is obtained. Along the direction which is parallel to the pixel, a grey level field map is averagely divided into p rows, then the grey level field map is averagely divided into q columns along the direction which is perpendicular to a pixel transverse direction, and thus p row by q column grids are generated by cutting the grey level field map. Each of the grids is internally provided with m rows and n columns pixels, the sum of m pixel grey level values of each column is calculated, and n sums are obtained. The maximum value of the n sums is obtained, and the corresponding column number is recorded and is a maximum value column number. The grey level value of the maximum value column number or the grey level values of one or two columns beside the maximum value column number are reserved, all reserved columns are defined as the bright line columns in the grid, the grey level values of other columns are set to be zero, the average grey level values of the bright line columns of p by q grids are calculated, and the grey level field map of the sheet light map with the elimination of dark lines is obtained.