The paper presents a method to detect Targets in synthetic aperture radar (SAR) images at a specified scene. Using the corresponding optical image of the specified scene, the potential regions of interests for Targets can be extracted off-line as a scene mask. Then, the SAR image can be co-registered with this scene mask and a change detector is used to detect the Targets only in the potential regions of the SAR image. Finally, the Targets can be located and detected with the change detection results. The experimental result shows that the proposed method can detect and locate airplanes well at the airport with a high resolution SAR image, and it obtains a high positive detection ratio and evidently decreases the probability of the false alarm. As a result, the proposed method fusing the SAR and optical data is appropriate in detecting airplanes at the airports, vehicles on the roads, ships in the harbours, and so on.