To improve the detection of infrared small target in the complex background,the target signals are generally enhanced by restraining the background.For the shortcomings of the isotropic background prediction method,a kind of anisotropic infrared background prediction method was proposed.According to the difference of local gradient features between the target and the background,the edge stopping function of anisotropic partial differential equation was improved.Then the mean of the two least direction values was set as the prediction value of the background,and the background gray level changed 0～255.Finally in order to extract the candidate target and reduce the false alarm rate of the target,the difference image was segmented by the method of constant false alarm threshold.Experimental results show that this method has a good background prediction,and it can effectively reduce the false alarm and improve the detection rate of the target.