The invention discloses a sustained-casing-pressure well mouth management and control device and an operating method. A sustained casing pressure value is monitored by means of a sustained casing pressure monitoring gauge, and sustained casing pressure data are recorded and monitored by means of a data acquisition unit; when the sustained casing pressure value reaches the maximum permissible sustained casing pressure value, an alarm device gives an alarm, and a sustained casing pressure relief electromagnetic valve is opened to release the pressure; when the sustained casing pressure is released to a recommended working pressure lower limit, the sustained casing pressure relief electromagnetic valve is closed; a sustained liquid injection valve is opened, a one-way valve of a sustained protective liquid storage tank is controlled, a centrifugal pump starts to work to pump protective liquid into a sustained space, and the flow rate of the sustained protective liquid is recorded by meansof an electromagnetic flow meter; the liquid level is monitored in real time by means of a liquid level monitoring device; and when the protective liquid pumped into the sustained space reaches a specific liquid level, the centrifugal pump automatically stops working, and the sustained liquid injection valve is closed. According to the sustained-casing-pressure well mouth management and control device and the operating method, the sustained casing pressure condition can be monitored in real time to provide reference for safe service of well shafts in high-acid gas fields; and the operabilityis high, the construction process is simple, and management and control of sustained-casing-pressure wells can be effectively implemented.