Aiming at the characteristics of the gun code image that characters are easy to wear and contrast gradient is too large or too small, a binarization method based on wavelet packet filter floating threshold and Niblack method is proposed. Firstly, the image is filtered using wavelet packet filter and binarized with the low pass image after filtering. Then, the image is binarized with the Niblack method to obtain the second fusing image. Finally, two fusing images are merged based on the minimum principle of image gray values to get the final binarization image. Experimental results show that the method has a good performance in binarization effect and adaptation range and can imply in many situation.