Abstract: With the rapid development of wind- photovoltaic-storage-hydrogen and other new energy power generation and power electronic technology, multi-type DC-DC converters with high transformation ratio and wide range are widely used, which brings a high challenge to the corresponding part in power electronics teaching. Facing with a wide variety of DC-DC converters with different styles, this paper took the bridge switching unit as the basic "cell unit", and adopted the idea of "cell unit-basic topology-evolutionary law", and used the cell unit to build a bridge between input and output conversion, so a normalized analysis method of DC-DC converter topology family was proposed. two basic Buck and Boost bridge switching units were proposed firstly and a unified drawing based on the cell unit was given for six non-isolated DC-DC converter topology. A thinking paradigm that used two Buck and Boost unit conversions to elaborate other converter topologies, commutation methods and voltage gains was proposed, in addition to which two switching units could be connected in parallel to form a bridge type bidirectional unit, which could then be extended to bidirectional, interleaved parallel, Boost/Buck DC-DC converters. For isolated DC-DC converters, four basic switching units are proposed from the concept of a transformer winding in series with power electronics device, namely a winding in series with a (single/double) switch(es)/diode(s). Based on the above ideas, this paper gives the construction process for flyback and forward, which is then extended to push-pull, single active bridge, dual active bridge, and N-phase interleaved parallel DC-DC converters. Since these converters have wide range of voltage gain, flexible series-parallel combinations, they are of great value for multiple types of DC-DC applications, and also build a bridge back to mapping engineering applications and theoretical knowledge from books.