Method for replacing wellhead and wellhead accessories under pressure

The invention discloses a method for replacing a well mouth and well mouth accessories under pressure. The method comprises the steps that S1, safety evaluation is conducted on a pre-construction well; s2, a wellhead square pit is dug, and a freezing box 3 is placed; s3, installing a high-pressure injection device 1 in a standardized manner, and connecting a high-pressure injection pipeline; s4, a refrigerant is added into the freezing box 3, and a temporary plugging agent is injected into the freezing box 3; s5, freezing slug positive/negative pressure testing; s6, a wellhead or wellhead accessories are replaced, and pressure testing is conducted; and S7, unfreezing the well mouth and recovering the original appearance of the well site. The well mouth hidden danger treatment mode is suitable for oil/gas/water wells, well killing is not needed in the operation process, open flow is not needed, a large amount of operation liquid is not generated, operation equipment is few, and the occupied area is small. 本发明公