Provided are a bypass type 220V grid voltage sag prevention device and a control method therefor. The bypass type 220V grid voltage sag prevention device comprises an AC-to-DC energy storage unit, a Single Chip Microcomputer (SCM) control and display unit, and an inverter output unit. The AC-to-DC energy storage unit comprises a rectifier circuit, an energy storage control circuit and a quick tank circuit; the SCM control and display unit comprises an SCM, a DC step-down module circuit and an energy storage voltage detecting circuit; and the inverter output unit comprises a high-frequency PWM generating circuit, a high-frequency transformer output circuit, a transformer output full-bridge rectifier circuit, a PWM generating circuit, a PWM driving and full-bridge inverter circuit, a 220V grid zero-cross point detecting circuit, a 220V grid voltage detecting circuit, a 220V grid and inversion AC converting circuit, and a signal interface circuit.