Abstract: SWISS rectifier is widely used in charging station, distributed DC power supply and other occasions due to its superior performance. Its main control goal is to maintain a stable output voltage on the DC side, a sinusoidal and symmetrical three-phase current on the AC side, and a unit power factor on the AC side. However, when the amplitude of the power grid drops, it is difficult to achieve the above three control objectives simultaneously based on traditional control methods. In order to effectively control the SWISS rectifier based on grid amplitude drop, this article introduces constant output voltage control (COVC) method and sinusoidal and symmetrical current control (SSCC) method, respectively. The former can achieve constant and non-fluctuating output voltage on the DC side, but cannot achieve sinusoidal and symmetrical current on the AC side. The latter can achieve sinusoidal and symmetrical current on the AC side, but cannot achieve constant and non-fluctuating output voltage on the DC side. On this basis. This article further proposes an improved coordination and optimization control (ICOC) method that combines the advantages of these two control methods. It can achieve coordinated optimization between a constant output voltage on the DC side and a sinusoidal and symmetrical current on the AC side, while maintaining a unit power factor on the AC side. The experimental results demonstrate that the ICOC method has significant advantages over COVC and SSCC, which is consistent with the theoretical analysis in this paper.