To address the casting process problem caused by the convergence of the inscribed circle radius of the axial flow fan blade trailing edge contour to zero, the existing blade trailing edge thickening structure is researched, and a new type of blade trailing edge rounding structure is proposed. Through establishing a numerical simulation model of the axial flow fan, the air flow rate, total pressure, impeller power, total pressure efficiency and noise of the fans with different trailing edge structures were analyzed by the computational fluid dynamics method. The results showed that the maximum air flow rate of the fans with different trailing edge structures gradually decreased with the increase of trailing edge thickness. For every 0.5 mm increase in trailing edge thickness, the maximum air flow rate of the fans with thickening structure and rounding structure was reduced by 0.72% and 0.68%, respectively. Under the designed air flow rate, for every 0.5 mm increase in trailing edge thickness, the impeller power of the fans with thickening structure and rounding structure was reduced by 1.92% and 1.87%, the total pressure was decreased by 3.04% and 2.84%, and the total pressure efficiency was reduced by 0.47% and 0.62%. When the thickness l of the thickening structure was 2.5 mm, the noise near the impeller was the minimum, reaching 105.41 dB, which was 0.79 dB lower than that at l=0 mm. When the fillet diameter D of the rounding structure was 3.0 mm, the noise near the impeller was the minimum, reaching 104.91 dB, which was 1.29 dB lower than that at D=0 mm. By quantifying the impact of trailing edge thickness variations on the performance of axial flow fans, the casting process problem of the blade is solved, which provides a reference for the structural design of the blade trailing edge and the optimization of its aerodynamic performance.