The molecular motor in microscopic quantum device is an important device in the field of micro-mechanical system and nanometer device. In this paper,the conditions and mechanism of one-way rotation are studied systematically. This paper analyzes the physical essence of macro ratchet work from the perspective of geometry. It obtains three necessary conditions. Two necessary conditions for one-way rotation of the microscopic ratchet read as follows: the non-equilibrium( internal) of the system and the proper ...