Learning transfer is a permanent theme in educational psychology and in the researching field of learning theories. Since a century ago, psychologists devoted themselves to the learning transfer research, but they could not reach a conclusion. Therefore, modern cognitive psychology proposes three learning transfer theories: component view of transfer, knowledge representation of transfer, and competence view of transfer. And accordingly three principles were put forward. It is believed that the recent researches do not only encourage the transfer learning research but also strengthen the belief of teaching for transfer.