It is well known that the fuselage and wing mainly consist of thin-skin stiffened panels and the failure load of stiffened panels is hot topic in aircraft engineering. Johnson-Euler equation is used to evaluate the failure loads, thus the effective width of skin needs to be determined. As for effective width of skin, there are several kinds of methods to calculate it so far. So this paper will focus on the calculation of effective width of skin, and quest for it's origin. Finally, the applicability of calculating methods is validated by test results，which is shown the calculation errors are less than 10 percent for the thin-skin stiffened panels. The results of the paper will be beneficial to engineers who design thin- skin stiffened panels in compression.