The utility model provides an annulus pressure monitoring and controlling means to deep sea seabed well head, has installed the lower piston including installing in the gas access department of installing the bottom above the department of gas access, and the lower piston passes through the connecting rod and links to each other with the upper piston, installs buffer below the upper piston, be provided with the gas outlet at the device, gas access department installs pressure sensor, and pressure sensor's output is connected PLC logic control unit and is connected the upper piston through power device, when gas access department fluidic pressure was higher than predetermined upper limit pressure value, the fluid promoted the lower piston rebound, made fluid passing through gases export outflow, carried out the pressure release, when the annulus pressure signal is less than predetermined pressure value, under the produced three kinds of condition of pressing fully of pressure, spring force and compressed fluid that the hydraulic pump provided for impress the casing annulus and carry out the ftercompction in the fluid passing through gases entrance of lower piston in will installing, the utility model has the characteristics of simple structure, convenient and practical, it is not perishable.