Currently, defogging algorithm based on dark channel prior is one of the most effective single image defogging method. This paper studies various image defogging technologies based on dark-channel-prior. The time complexity of soft matting algorithm is too large. This paper presents an adaptive median filter to achieve a smooth and refined transmittance to improve the algorithm speed and a robust method for determining the value of Light Atmosphere. Experimental results show that the proposed method can achieve effective defogging, ensure defogging image clarity, and increase speed of dark-channel-prior defogging algorithm, which has some practical value.