Objective To observe and evaluate the efficacy and safety of two years sublingual Dermatophagoides Farinae Drops of specific immunotherapy in children with asthma. Methods 110 children aged 6~14 years old with acute exacerbation of mild-moderate allergic asthma from Department of Asthma bronchitis of Fuzhou Children's Hospital were selected and divided randomly into experimental group and control group of 55 cases each from October to December in 2009.The experimental group was given to sublingual Dermatophagoides Farinae Drops and conventional treatment in accordance with the GINA,control group was given conventional treatment in accordance with the GINA.IgG4,sIgE,skin prick test,FEV1% and the PEF of pulmonary function test,and the security were detected before and after treatment of 6 months or 12 months through 2-year follow-up. Results 1)The FEV1% of lung function,the value of IgG4 and the score of C-ACT in experimental group were higher than control group for 24 months treatment,and the score of the day night time asthma symptom was lower than the control group(P＜0.05);2) The dust mite skin test level changes,sIgE and the PEF values of lung function for 24 months treatment in the experimental group showed no differences with the control group(P＞0.05);3)The value of IgG4 in experimental group increased year by year between treatment for 12 months and 24 months,the difference of IgG4 between the experimental group and the control group was statistically significant (P<0.000 1); Conclusions The improvement of the lung function of children with allergic asthma,the score of the day night time asthma symptom and the score of C-ACT in experimental group are better than the control group.The IgG4 value is increased significantly year by year in the specific immunotherapy of sublingual dust mite for two years.Dermatophagoides Farinae Drops is a safe and effective treatment of allergic asthma in children-specific immunosuppressive drugs.