Solution-mediated polymorphic transformation (SMPT) exists extensively in crystallization from solution in many polymorphic systems. To obtain the desired products, it is crucial to understand the mechanism of the SMPT process and then to develop a regulation strategy for it. However, the mechanism of SMPT of different polymorphs is still not well understood. In this work, the mechanism and control strategy of SMPT were studied in detail by using 5nitrofurazone as a model compound. A series of SMPT experiments were carried out. Different 5-nitrofurazones form β (different sizes or with different amounts of impurities/additive) can (1) transform to form α directly, or (2) transform to form γ directly, or (3) initially transform to mixture of form α and form γ and then finally transform to form γ. Then, the mechanism of the SMPT process of 5-nitrofurazone was explored by using quantum chemical calculation, solubility determination, lattice energy calculation, single crystal indexing, and lattice matching calculation. Finally, the regulation strategy of the SMPT process of 5-nitrofurazone was proposed: form α can be obtained through decreasing size of form β. Form γ can be directly obtained through the addition of a certain amount of 5-nitrofurfural.