A valve mechanism includes a valve, a camshaft, a fixed support, an intermediate swing arm and a supporting base. The fixed support is provided with a connecting-portion via hole running from top to bottom, two oil passages are defined in a connecting portion, and each of the oil passages is connected with the connecting-portion via hole and a corresponding intermediate swing arm shaft hole. The supporting base defines first and second oil feeding passages therein, the first supporting-base oil feeding passage is communicated with the connecting-portion via hole, and an upper end of the second supporting-base oil feeding passage extends to a base-body camshaft supporting portion of the supporting base. An engine and a vehicle are also provided.