Abstract: Based on the hypothesis that the changes of the growth line number of nautilus’s shell reflect the changes of the moon’s cycle around the earth as time goes by, we draw two conclusions by the method of extrapolation: 1 The distance between the earth and the moon at first when the moon revolves around the earth which capture it is one fifth of that today. 2 It has been 7×108 years since the moon was captured by the earth at first. These support helpful enlightenment for far study about relation between the earth and the moon.