To evaluate the efficacy and onset time of single dermatophagoides farina sublingual immunotherapy in patients sensitized to dermatophagoides farina (Df) and dermatophagoides pteronyssinus (Dp), discuss the mechanism of single allergen immunotherapy in polysensitized patients and provide evidence for clinical applications.This is a retrospective study, we screen 50 patients with allergic rhinitis sensitized to Df and Dp in our department. The average age of those patients is 28.98 +/- 2.41 years old. The nasal symptom scores of sneezing, itching, obstruction and runny nose are recorded after three to six months. SPSS 20.0 software is used to analyze the data.After treatment for 3 months with sublingual immunotherapy, the TNSS (P < 0.05), score of sneezing (P < 0.01) and runny nose (P < 0.01) is significantly decreased comparing with that before treatment. The scores of obstruction and itching are increased, but the differences are not statistically significant. After treatment for 6 months, the TNSS (P < 0.01), score of sneezing (P < 0.01), itching (P < 0.01), obstruction (P < 0.05) and runny nose (P < 0.01) are all decreased, the difference between the scores of 6 month after treatment and that before treatment is statistically significant. And all of the scores (Z = -5.749, P < 0.01, sneezing; Z = -5.353, P < 0.01, runny nose; Z = -3.476, P < 0.01, congestion; Z = -3.824, P < 0.01, itching; Z = -5.746, P < 0.01, TNSS) at 3 month after treatment are significant higher than that after 6 month treatment.The onset time of single Df sublingual immunotherapy for patients sensitized to Dp and Df with allergic rhinitis is 12 weeks, and the efficacy is enhanced as time of the treatment.