Abstract: An image fusion algorithm based on gradient pyramid is proposed which takes advantage of image characteristics of underwater sonar environment .First，the gradient pyramid transform was imposed on registrated sonar images .Second，an activity and match measure were constructed based on the local neighborhood of the images. The local neighborhood feature of images was considered as a fusion strategy. Finally，the fusion image was obtained through synthesis module and multi-scale inverse transform. Experiments revealed that the new algorithm is effective under objective evaluation criteria in the absence of a standard reference image.