In this study, the effectiveness of solid insulating layers on AC breakdown strength of small, non-uniform air gaps was both theoretically and experimentally investigated. Electric field and potential distributions with and without dielectric barriers have been analyzed by using the finite element method (FEM). Breakdown voltage characteristics of rod-to-plane air gaps, up to 50 mm, were achieved for various surface area, thickness, and position of barriers. Silicone rubber (SiR), polyvinyl chloride (PVC), and mica barriers were located horizontally between the electrodes to observe the effect of dielectric obstructions on breakdown voltage. Flashover tests were both conducted for varying air gaps, barriers positioned on the grounded electrode, and a constant gap with floating barriers. The results of simulation studies and breakdown tests have been discussed in accordance with the physical principles of discharge phenomena. In conclusion, AC flashover characteristics of air gaps were comprehensively analyzed due to the size, material, and position of dielectric barriers.