This paper aims to investigate the impact of small-sized cutting serrated trailing edges on airfoil aerodynamic noise and to analyze the influence of the relationship between height and trailing edge boundary layer thickness on noise reduction effectiveness. Taking the NACA0012 airfoil as the research object， a hybrid computational aeroacoustics method was employed for simulation. Noise experiments on the NACA0012 airfoil were conducted at a wind speed of 20 m/s to validate the accuracy of the simulation method. By controlling the height and width of the serrations， the effect of different serrated trailing edge shapes on airfoil aerodynamic noise at angles of attack of 0° and 10° was studied. The results indicate that the noise reduction effect of serrated trailing edges is proportional to both height and width. The maximum noise reduction at a 0° angle of attack is 3.3 dB， while at a 10° angle of attack， it is 2.6 dB. The cutting serrated trailing edge structure increases the high-frequency components of flow noise， especially at a 0° angle of attack. Compared to embedded serrated trailing edges， cutting serrated trailing edges has a smaller limit for maximum noise reduction height.