Introduction: Severe asthma has a poor response to hormone therapy and a poor level of control, so the discovery of new pathogenetic mechanisms is important for diagnosing and treating severe asthma. IL-35 may play a protective role in autoimmune diseases by directly or indirectly inhibiting the secretion of IL-17, which is an important proinflammatory factor involved in the occurrence and development of autoimmune diseases. The autologous serum skin test (ASST) is a good sensitivity and specificity screening test for autoimmune functional autoantibodies. We compared the levels of IL-35 and IL-17 in serum samples, the positive rate of ASST, the level of exhaled nitric oxide (FeNO), and the atopic constitution in patients with severe asthma to those with mild-to-moderate asthma so as to explore the possible autoimmune pathogenesis of severe asthma. Methods: Patients with mild-to-moderate and severe asthma were enrolled. Their age, gender, smoking history, family history of asthma, history of allergic rhinitis, positive allergen results, serum total IgE (TlgE), allergen-specific IgE (slgE), routine blood, ASST results, and FeNO test results were compared and analyzed. The IL-35 and IL-17 levels in serum samples from both groups were measured by enzyme-linked immunosorbent assay for comparison and analysis. The SPSS 22.0 software package was used for statistical analysis. Results: A total of 50 patients with mild-to-moderate asthma and 31 patients with severe asthma were included in this study. The proportion of patients with a history of smoking and a family history of asthma was significantly higher in the severe asthma group compared to the mild-to-moderate asthma group (all p < 0.05); the number of positive allergen tests was significantly lower in patients with severe asthma compared to those with mild-to-moderate asthma (p < 0.001). The rate of positive ASST was significantly higher in patients with severe asthma than in patients with mild-to-moderate asthma (p < 0.05). Serum IL-17 levels were significantly higher in patients with severe asthma than in patients with mild-to-moderate asthma (p < 0.05), but serum IL-35 level between the two group was not significantly different (p = 0.113). ASST-positive patients had a statistically significant increase in the risk of developing severe asthma, while patients with allergen positive were less likely to develop severe asthma (positive ASST: OR = 5.277, p = 0.024; allergen positivity: OR = 0.123, p = 0.001). Conclusions: IL-35 has a weaker inhibitory effect on high IL-17 expression in patients with severe asthma, and the rate of positive ASST was significantly higher in patients with severe asthma, which all suggested the possibility of autoimmune pathogenesis in patients with severe asthma.