Studying on 94 severe level asthma patients, treating at Allergology and Immunology clinical Department, Bach Mai Hospital year 2007-2008. The author realize that there is a change in the clinic symptoms: the eosinophil rate in blood and sputum highly increase 4 - 7 times compare with the normal person, the value of PEF is about 21/p, PaCO2 increase over 45 mmHg, PaO2 decrease less than 60 mmHg, SpO2 decrease less than 75 mmHg, value of respiratory function index: PEF, FEV1, FEV1 percent decrease to 60 percent and MEF less than 50 percent (compare to theory).