  For the past decades, the low-temperature phase of Ca$_3$Ru$_2$O$_7$ below
the 48K first-order phase transition remains a puzzle with controversial
suggestions involving metallic ferroelectric, orbital or magnetic ordering.
Through analysis of experimental lattice structure, density functional theory
calculation, and effective model analysis, we propose that the 48K phase
transition is a bond formation transition promoted by the magnetism mediated
orbital re-polarization. Most interestingly, this transition is accompanied by
a switch of \textit{two} metallic ferroelectric orders from a $xy+y$ symmetry
to $xz+z$. Our study not only resolves a long-standing puzzle of this phase
transition in this material, but also demonstrates perhaps the first example of
transition between multiple emergent ferroelectric orders in bad metals,
resulting from interplay between multiferroic orders.
