A dome-based cyclic inert sealing system for storage of bulk liquid hazardous chemicals, the system comprising: an external floating roof tank, a dome structure, an inert sealing pipeline, and a gas source servo device; wherein the dome structure is formed by a top portion of a tank wall of the external floating roof tank for sealing; the dome structure together with an internal wall of the external floating roof tank, a floating plate and a sealing device form a gas phase space which is isolated from atmosphere, so as to fill the gas phase space with an inert sealing medium; the inert sealing medium is a gas fire-fighting medium used in a suffocation fire-fighting method; the gas source servo device is connected to the gas phase space through the inert sealing pipeline and communicates through a valve for feedback-controlling states of the inert sealing medium in the gas phase space; wherein the gas source servo device comprises a servo constant voltage unit, the servo constant voltage unit comprises an inlet gas compressor, a pneumatic check valve, a gas source container, and an outlet gas valve component, wherein: the inlet gas compressor is controlled to be started or stopped in a manual mode, a linkage mode and\or an automatic mode, so as to transfer, compress and load the inert sealing medium in the gas phase space into the gas source container, as well as feedback-control a pressure of the inert sealing medium in the gas phase space to be no higher than a preset pressure parameter; the pneumatic check valve matches a rated outlet pressure of the inlet gas compressor, and is arranged on a pipeline between an outlet side of the inlet gas compressor and the gas source container, so as to cooperate with the gas source container for storing a working gas and saving a pressure potential; the gas source container matches a rated inlet pressure of the inlet gas compressor and a preset storage volume, so as to provide and store the inert sealing medium which is cyclically inputted into the gas phase space; and the outlet gas valve component is controlled to be opened or closed in an independent mode, an automatic mode, a linkage mode and\or a manual mode, so as to throttle and decompress the inert sealing medium in the gas source container before being released into the gas phase space, as well as feedback-control the pressure of the inert sealing medium in the gas phase space to be no lower than the preset pressure parameter; and wherein the servo constant voltage unit further comprises a servo temperature control component which comprises a temperature transmitter, an inert sealing medium cooling device and an inert sealing medium heating device; the temperature transmitter is installed in the inert sealing pipeline and communicates with the inlet gas compressor and/or the outlet gas valve component directly or through a control system, so as to detecting a temperature variable of the gas phase space in real time and transmit a preset temperature parameter signal for starting or stopping the inlet gas compressor, or for opening or closing the outlet gas valve component; the inert sealing medium heating device is installed in the outlet gas valve component. the inlet gas compressor is controlled to be started or stopped in a manual mode, a linkage mode and\or an automatic mode, so as to transfer, compress and load the inert sealing medium in the gas phase space into the gas source container, as well as feedback-control a pressure of the inert sealing medium in the gas phase space to be no higher than a preset pressure parameter; the pneumatic check valve matches a rated outlet pressure of the inlet gas compressor, and is arranged on a pipeline between an outlet side of the inlet gas compressor and the gas source container, so as to cooperate with the gas source container for storing a working gas and saving a pressure potential; the gas source container matches a rated inlet pressure of the inlet gas compressor and a preset storage volume, so as to provide and store the inert sealing medium which is cyclically inputted into the gas phase space; and the outlet gas valve component is controlled to be opened or closed in an independent mode, an automatic mode, a linkage mode and\or a manual mode, so as to throttle and decompress the inert sealing medium in the gas source container before being released into the gas phase space, as well as feedback-control the pressure of the inert sealing medium in the gas phase space to be no lower than the preset pressure parameter; and wherein the servo constant voltage unit further comprises a servo temperature control component which comprises a temperature transmitter, an inert sealing medium cooling device and an inert sealing medium heating device; the temperature transmitter is installed in the inert sealing pipeline and communicates with the inlet gas compressor and/or the outlet gas valve component directly or through a control system, so as to detecting a temperature variable of the gas phase space in real time and transmit a preset temperature parameter signal for starting or stopping the inlet gas compressor, or for opening or closing the outlet gas valve component; the inert sealing medium heating device is installed in the outlet gas valve component.