A novel method is proposed to obtain the target depth. A sequence of images is taken by linear camera arrays spreading perpendicularly to the line of sight. The image from the camera at the intersection of the linear camera array and the line of sight is selected as the reference image. The measurable range is divided into several distance segments. For each segment, a parallax correction stack image is calculated, then the regional similarity of the reference image and the stack image is got. The target distance is in the segment which has maximum similarity of the reference image and the stack image. Without image matching, depth from synthetic aperture focus has good robustness and cannot be influenced by single image error or deviation. Simulation results verify the efficacy of this scheme. Moreover, the range precision is also analyzed. Without electromagnetic pollution, the method has the advantages of concealment.