[(CH3)(2)NH2][Mn(HCOO)(3)],　an　organic-inorganic　perovskite-like　hybrid　multiferroic,　shows　promising　aspirations　for　the　next　generation　magnetic　storage　devices,　light-weight　chips,　optical　devices,　etc.　However,　the　growth　of　centimeter-sized　large　single　crystals　of　[(CH3)(2)NH2][Mn(HCOO)(3)]　remains　a　big　challenge.　Herein,　we　report　a　facile,　environmentally　friendly　approach　to　grow　[(CH3)(2)NH2][Mn(HCOO)(3)]　single　crystals　whose　size　could　be　up　to　10　x　9.61　x　3.6　mm,　the　biggest　one　ever　reported　to　date.　In　addition,　high-pressure　Raman　spectra　of　the　material　exhibited　the　existence　of　three　high-pressure　polymorphs　at　2.1,　4.1,　and　6.7　GPa.　The　high-pressure　phase　transitions　are　associated　with　highly　distorted　frameworks,　and　the　phase　under　a　pressure　larger　than　6.7　GPa　induces　large　structural　changes　in　the　hydrogen　bond-related　interactions,　which　is　different　from　the　highly　ordered　low-temperature　monoclinic　ferroelectric　phase　(Cc)　observed　at　ambient　pressure.　Our　studies　may　shed　light　on　the　phase　transition　mechanisms　of　the　multiferroic　metal-organic　framework　[(CH3)(2)NH2][Mn(HCOO)(3)]　under　high　pressures.