This paper studies the binarization technique of QR code image and proposes an improved background gray-level based algorithm for uneven illumination QR code image. Firstly, it cuts the QR image as several blocks based on the size of original image, then evaluates the gray-value of each block and set block's gray-value with the bilinear interpolation method. Thirdly, it subtracts the estimated background image from original uneven illumination image get the corrected image, and with this method to eliminate the bad affection for binarization from nonuniform illumination. Experiments show that the algorithm can get a better QR binary image effectively for QR code image which has widespread gray-level and especially for uneven illuminated QR code image.