This invention provides an adjustable oral interface for adapting a user's oral anatomy to deliver a negative pressure generated by an oral negative-pressure therapy system. The adjustable oral interface comprises a shield adapted for being situated between a user's lips and front teeth, a negative pressure deliverable part coupled with the shield, and a tube fluidly communicated between the negative pressure deliverable part and a negative pressure generation source. The negative pressure deliverable part is adapted for being adjustably situated at a space between the user's tongue and upper palate so as to be conformable to the contour of the upper palate, whereby the adjustable oral interface delivers negative pressure via the negative pressure deliverable part to the front and back of the user's oral cavity to eliminate air space between the tongue and the upper palate.