An optical element adjustment mechanism is for loading a reflection optical device, which comprises a base and a loading element. The base is movably assembled to the reflection optical device. The base is a hollow tubular structure, and each side has an opening. The inner edge of one of the opening has a plurality loading surfaces extension to the central side, and two leaning surfaces protruded along a tube wall of the base. The loading element movably assembled to the base has a first surface, a second surface and two datum planes. The first surface is flattened against the plurality loading surfaces. The second surface has a connecting portion connected the optical element. The two datum planes are respectively flattened against the two loading surfaces. Wherein, at least one adjustment gasket is moveably assembled between the base and the loading element for precision adjustment.