According to the disadvantage of presented automatic optic inspection (AOI) equipments with the weaker image preprocessing function, an image enhancement method of printed circuit board (PCB) based on morphological filtering is proposed. Firstly, the colorful images captured by AOI equipments using the average value rule are grayed. And then the image enhancement is performed using morphological filtering method based on the grayed images. The method is realized using C# programming language under VS2008 development platform finally. Experimental results show that noise points can be removed effectively by the method and the detailed features of the original image are reserved, so good effects are achieved.