A flip-up cover mechanism. An annular body includes two opposite through holes. A displacing member is disposed in the annular body and includes two opposite push portions and a first flange. The push portions respectively protrude from the annular body via the through holes. A cover is rotatably connected to the annular body and includes a second flange detachably engaged with the first flange. A torsion spring is connected between the annular body and the cover. When the second flange is engaged with the first flange, the cover is closed in relation to the annular body and the torsion spring is twisted to provide restoring resilience. When the push portions are respectively pushed through the through holes, the displacing member is elastically deformed to separate the first flange from the second flange and the cover is lifted from the annular body by the restoring resilience provided by the torsion spring.