The SCO phenomenon exhibits significant aggregation-dependent behavior between isolated molecule and cooperative supramolecular interaction. It is crucial for complete control of the variables that affect the spin switching based on aggregology for precision design of SCO materials, including the contribution of the nature of the ligands, the non-coordinating anions, the solvent molecules and the crystal packing. Herein, we report the aggregate-responsive spin crossover switching in a spin-labile iron(II) complex Fe(HL) 2(NCS) 2·2DMF ( 1), where HL adopt an intermediate pyridyl benzimidazole ligand, namely methyl 2-(2-Pyridinyl)-1H-benzimidazole-6-carboxylate. The SCO behavior of 1 can be on-off between solution and crystallization. By introducing poor solvents to achieve aggregation control, it was found that compound 1 exhibits aggregation induced spin crossover switching. Meanwhile, because of the spin-labile iron(II) nature in 1, a reversible proton-induced magnetic response in sold and solution was fully investigated by Faraday method and Evans’ method, which indicated the completely reversible switching from low-spin to high-spin in accompany with the optical response.