The invention discloses a machining method of a sealing composite rubber ring long in service life. The machining method comprises the following steps of (1) metal ring treatment, (2) natural rubber modification treatment, (3) composite preparing, (4) raw material weighing, (5) mixing treatment and (6) machining forming. According to the preparation method of the sealing composite rubber ring, theprocess is simple, steps are matched reasonably, and application and popularization are facilitated; and the prepared sealing composite rubber ring has the advantages of being high in stability, highin wear resistance and corrosion resistance, not prone to being damaged, long in service life and the like and has great market competitiveness and productivity effects.