“One Prescription with Two Directions” is a medication method that means prescriptions constituted by the same herbal medicines have diverse efficacy of prescription as the differences of dosage forms，doses，decoction methods or methods of taking medicine. The thought is as the same as the statement of “the formula of the prescription” said by Ke Yunbo，which means the basic group structures of the prescriptions are as usual，as well as adding or subtracting some herbs of the prescriptions appropriately on the basis of accompanying syndromes. Thus，it can lead to several changes of the efficacy and the treatment effects of prescriptions. It contains 5 probabilistic methods founded by Zhang Zhongjing and the addition or subtraction of the formulas noted after the prescriptions，such as taking Lizhong Bolus as decoction method，and so on. It is indispensable to point out that the “two” of “One Prescription with Two Directions” means not only the number of “two”，but also “One Prescription with Three Directions” or “four directions”. Its meaning is “many”. The reasons for changing the directions are dominated by the depth of pathogenic factors，the vicissitude of vital qi and pathogens，and the imparity of accompanying syndromes. The purport of this paper is to illustrate some typical examples in Treatise on Febrile Diseases and Synopsis of Golden Chamber to discuss the application of the thought of “One Prescription with Two Directions”，so as to enlighten the train of thought to use the classical prescriptions neatly and improve the efficacy.