This article summarizes the design and development of DC-DC autotransformer(DC AUTO), a new type of DC-DC converter. The prior art of DC AUTO is firstly described, and then the development of DC AUTO and its supported technologies are summarized. Analogy between AC autotransformer and DC autotransormer is investigated. The converter cost and power loss ratio of DC AUTO with bidirectional DC fault isolating capability are studied. A number of extended technologies such as multiport DC AUTO, hybrid DC AUTO, unidirectional DC AUTO and grid interconnector are summarized, pointing out that under low and medium stepping ratio, the DC AUTO technology is able to replace the conventional DC/AC/DC technology.