In a precision testing method of an optical lens using a computing device, the computing device is connected to an imaging system. The computing device controls the imaging system to generate an image of an object according to light rays reflected from the object and collected by the optical lens. A dimension of the object is measured from the image. A maximum value and a minimum value of the dimension of the object are determined. A difference between the maximum value and the minimum value is calculated. According to the difference, it is determined whether the optical lens agrees with a precision requirement.