The invention relates to a modification method for adjusting pressure of a single-hole carbonization chamber in an existing coke oven. The modification method includes 1), mounting a pressure measurement pipe guide sleeve on a bridge pipe, penetrating a pressure measurement pipe into the pressure measurement pipe guide sleeve to enter the bridge pipe, enabling the extending end to be located at the spraying range of an ammonia water spray nozzle, mounting an actuator on a gas collection pipe operating platform or a gas collection pipe, connecting the power output end of the actuator with a moving rod of a water-sealed valve disc, and connecting the pressure measurement pipe and the actuator with a computer control system; 2), according to different quantities of raw coke oven gas, generated in different working periods, of the coke oven, adjusting the pressure of the bridge pipe based on three adjustment stages, namely earlier stage, middle stage and last stage, and enabling the pressure in the carbonization chamber to be constantly kept micro positive from coal feeding to coke discharging. The modification method has the advantages that the existing coke oven can have a function of automatically adjusting the pressure of the single-hole carbonization chamber; the structure and the method are simple and easy, the modification method is quite suitable for modification of existing coke ovens, and modification without oven shutdown can be realized.