Transfer alignment is one of the key techniques in modern inertial guidance weapons. In this paper，principle of transfer alignment is introduced. Theory and methods in transfer alignment technology are thoroughly summarized，including error models of inertial navigation system，matching methods，observability analysis，filtering algorithms，error compensation techniques，simulation and experiment methods，et al. A usable mathematic model for transfer alignment is presented. From the point view of accuracy，rapidness and robustness，progresses of transfer alignment technology in the past few years are analyzed and synthesized. Difficulties and prospects in transfer alignment are also discussed.