Objective To explore the biomechanical mechanism of aortic valve insufficiency (AI) after single valve replacement (AVR) in children and propose countermeasures. Methods The idealized aortic valve model and postoperative growth model were constructed. By changing the length of the free edge of the leaflet, the height of the leaflet and a concave structure with improved design, finite element analysis was used to compare the effects of different structure dimensions on the movement synchronization and closing performance of the aortic valve after surgery. Results The closure of the replacement leaflet lags behind the autologous leaflet, which fits 2 mm below the free edge of the replacement leaflet. The AI occurs 6 years after operation. Increasing the height of the leaflet cannot improve the postoperative effect and will increase the maximum stress of the leaflet. Increasing the free edge length by 10% can improve postoperative outcomes, when increasing the free edge to 15% will cause the leaflet to be too long, and hence result in a poor fit of the aortic valve. Compared with the traditional structure, the concave structure is more conducive to aortic valve closing performance, and it can effectively reduce the maximum stress by 20% with the best effect. Conclusions The movement of the leaflet will be out of synchronization after AVR, the point of convergence will be shifted, and AI will appear 6 years after surgery. It is recommended to cut to a concave structure with the free edge increased by 10%, while increasing the height of the leaflets is not recommended.