Abstract: To address the scarcity of single-phase multiferroic materials, this study proposed a new method for designing multiferroic materials by introducing magnetic ions at the B site based on the polar organic-inorganic hybrid perovskite structure. Using first-principles calculations, this study designed a type of organic-inorganic hybrid perovskite multiferroic material, namely (NH₂NH₃)Cr(HCOO)₃, and systematically studied its ferroelectric and magnetic properties. Results show that its ground state is an orthorhombic phase with Pna2₁ symmetry, capable of simultaneously exhibiting ferroelectricity and A-type antiferromagnetism. The ferroelectric polarization measures approximately 2.60 μC/cm², with contributions of 18% from the NH₂NH₃⁺ organic cation, 72% from the Cr(HCOO)₃^- framework, and 10% from their coupling. Additionally, this study conducted a detailed investigation of the ferroelectric-to-antiferroelectric phase transition and ferroelectric polarization reversal, by constructing intermediate state structures, calculating total energy and polarization intensity, and providing preliminary predictions on the energy barrier size and possible transition pathways.