A height adjustment mechanism includes a fixing member, an adjustment member rotatably engaging with the fixing member, and a standard member having a standard surface. The adjustment member defines an engaging hole. The standard member defines an alignment hole through the standard surface corresponding to the engaging hole of the adjustment member. The standard member is separately positioned over the adjustment member, and the standard surface of the standard member contacts with one distal end of the adjustment member. An assembly method for an electronic device is also provided.