A grey level model of small targets in the spatial domain is established on the basis of the point spread theory in target imaging. The basic characteristics of the target, background and noise are analyzed. After the open and close morphologic operation is implemented, the grey level variation in each pixel position is derived. Thus, the potential target areas are determined. The multi-orientation and multi-degree gradient of each potential area are studied. The detection of small targets is implemented in a single frame. The result shows that this method can effectively suppress uneven background clutter, enhance target signals and improve the detection of bright and dark small targets in a single frame. For an image with a signal-to-noise ratio (SNR) of 0.89, a SNR gain of 34.74 can be obtained.