Wu Ling San syndrome is not a dangerous syndrome, but its real pathogenesis is often neglected by people. The viewpoint of ”stagnated fluid in bladder” is not real. The application of Wu Ling San can not satisfy it clinically. The author uses Zhongjing Article to find out that the mechanism of Wu Ling San is associated with spleen and stomach, where the dampness can't be dispelled due to dysfunction of stomach and spleen, so the inhibition of the qi mechanism in sanjiao is occurred to get thirst, and dysuria. New explanation of Wu Ling San is propose, to describe that Wu Ling San syndrome can not be described from Urinary Bladder Meridian of Taiyang. It is the disorder caused by loss of regulation of the stomach & spleen in middle jiao. The mechanism of Wu Ling San can be understood well to grasp the application time for clinical treatment precisely.