Abstract: A method for injecting non-condensable gas or application of in-situ combustion to recover remaining oil in a heavy oil reservoir with bottom water includes: drilling a new horizontal well in an oil layer between the existing horizontal production well location and the bottom water layer; preheating the new horizontal well; after the horizontal section of the horizontal well is in thermal communication with the upper steam/gas chamber, performing gas injection in existing wells to maintain pressure slightly higher or similar to the pressure of the bottom water layer, and converting the horizontal well into a continuous production well; drilling a vertical well in the unswept reservoir area; establishing a fluid communication in the oil layer between the vertical well and the horizontal well, injecting air or oxygen into the vertical well; and in the later stage of the horizontal well, stopping gas injection and gradually reducing the pressure in the steam/gas chamber.