According to the stitching structure of CCDs in an Aerial Push-broom Remote-sensing Camera (APRC), an auto-focus method by using the image from the CCD overlapped sections was proposed. Firstly, the structure of CCD in the APRC was introduced. Based on the pushing-broom imaging characteristics, a Field Programming Gate Array (FPGA) which can process data in parallel model was used to receive the image data from multi-CCD overlapped sections and calculate the evaluation values of image quality at the same time. Then, three kinds of the CCD overlapped sections with the biggest evaluation values of image quality were selected as the gist for determining the focus direction. Finally, the feasibility of the method proposed was validated by an experiment. In the experiment, when the push-broom frequency is 10 kHz, the time for one focus step is 0.2 s, which illuminates that the proposed focusing method has good real-time ability, and it can offer a feasible gist for the on-track focus in the APRC.