In order to protect the image edge details while filtering out the image salt and pepper noise, an image salt and pepper noise filtering algorithm based on connectivity detection is proposed. Since the gray value of the salt and pepper noise point tends to be different from the gray value of the normal pixel point, the algorithm compares the pixel point gray value with the gray value of the neighborhood pixel point to make the pixel point with larger difference. It is listed as a suspected noise point, and then it is judged whether the point is a noise point by detecting whether the suspected noise point is a part of the image connected area. The noise point is finally filtered out by the median filter. The algorithm can effectively distinguish the edge of the image area from the salt and pepper noise. The experimental results show that the algorithm can effectively remove the salt and pepper noise with the density ranging from 0 to 0.9. The peak signal-to-noise ratio of the algorithm can still reach 30 dB with the noise density of 0.9. It satisfies the requirement to effectively remove the salt and pepper noise of different density ranges while protecting the image details.