Purpose: To approach to pathological essence and treatment principle of syndrome of Qi system of epidemic febrile disease. Methods: 60 rabbits were randomly divided into normal group

control group . clearing away Qi group

clearing Qi and nourishing Yin group

clearing away Qi and removing blood stasis group

and clearing away heat and blood stasis and nourishing Yin group. Symptoms and signs

body temperature

laboratory correlative indexes and pathological morphology of viscera and tissues were investigated. Results: The symptoms was the mildest and the heat state was the lowest with less drinking

and the MPAR decreased. PT and KPTT prolongated in the clearing away heat and blood stasis and nourishing Yin g;roup; plasma protamine paracoagulation test in both the control and clearing away Qi groups were positive

and in the clearing away heat and blood stasis and nourishing Yin group only 10% was positive with a significant difference as compared with the control group and the clearing away Qi group in activity of PLg （ P<0. 01） : the pathological lesion of blood stasis

bleeding and inflammation in the viscera and tissue in the clearing away Qi and nourishing Yin group and the clearing away Qi and blood stasis group were milder

and the mildest in the clearing away heat and blood stasis and nourishing Yin group. Conclusion: The essence of the pathological changes of syndrome of Qi system are heat excess

blood stasis

insufficiency of Yin. and the treatment principle is clearing away heat

removing blood stasis and nourishing Yin.