The utility model discloses a twin columns magnetic cores structure's planar transformer, ferrite planar transformer magnetic core and multilayer plane winding coil including " pi I " structure, the utility model discloses not only reduce the whole thickness of magnetic core but also guaranteed whole magnetic circuit flux density's equilibrium, simultaneously, effectual shielding of solving the planar coil magnetic leakage, it can set up magnetic air gap outside all planar coil windings, has avoided being in the influence that air gap plane winding was led to the fact by the air gap effect, the utility model discloses make flat transformer no longer because of restricted by coil turns, and pursue frequency of operation's improvement simply to lead to a great deal of technological difficulties such as power efficiency reduces, electromagnetic compatibility is very difficult up to standard.