Machine Vision was used to observer and measure the underwater bubbles. There are several ways been taken to solve many difficulties in the process of the acquisition to get the image. Such as the equipment selection, the light sources selection, the approach to images and the feature extraction of the image. The most important of them is the noise elimination and the extraction of the bubbles. The feature of the image can be very obviously after the Median filter and Sub-pixel edge detection. In this way, it provided an effective and feasible method to measure the underwater bubbles.