The present invention provides a method of testing moisture retention of tobacco in which dynamic rules on moisture desorption of the cut tobacco in a dry environment are investigated by using a dynamic vapor sorption system and has found that a dry basis moisture content at an earlier stage of moisture desorption of the cut tobacco has a preferred linear correlation with a square root of time. The database controlling system includes an external file for storing data, such as long and massive data, not ordinarily operated, an external file controlling device for controlling the external file, and an external file list storage file for storing a list of the external files. Thus a desired range of the grayscale can be corrected.