We usually know that the Chinese medicine decoction twice, known as the first and second decoction, and then mix the two to take, but we do not notice why it is necessary, some people want to save time, want to extend the decoction time of the method instead of the second decoction, but this method is wrong. Chinese medicine decoction process of active ingredients gradually by the internal medicine to the soup gradually dissolved, but the drug is not always dissolved, when the concentration of internal and external to reach equilibrium, will stop dissolving or dissolving slow, this is must be filtered out of the medicine, and then add water for the second decoction, the establishment of a new concentration of the difference, so that the drug continues to dissolve. And some drugs in water solubility is smaller, more difficult to dissolve, generally have to have two decoction to dissolve, if only a decoction is more difficult to dissolve, increase the time of decoction in time, the active ingredient is still dissolved less, therefore, Chinese medicine can not be a long time instead of two decoction.