The motional electromotive force in the electromagnetic induction phenomenon plays a very important role in the general physics course, the discussion of its generation mechanism in mainstream textbooks believes that it is closely related to the Lorentz force experienced by the free electrons inside the conductor rod which moves to cut the magnetic field line, but the two statements in the textbook are not entirely reasonable. Based on the classical microscopic images, we discuss the action of the free electrons and the surrounding particles and make a detailed analysis of the generation mechanism of motional electromotive force, reveal the accurate relationship between motional electromotive force and Lorentz force, and clarify some misunderstandings about the relationship between them.