Organic metal halides (OMHs) have attracted extensive research interests due to their interesting photoluminescent properties. However, to date, most OMHs have been synthesized through the trial-and-error method, and it remains a big challenge to control the molecular-level structures through directed synthetic approaches to rationally optimize luminescence properties. In this work, we proposed a crystal structure modulation strategy to control the dimensionality and optical properties of OMHs by increasing the packing density of Pb-Br octahedra via altering the precursor stoichiometry. By precisely adjusting the ratio of 3-aminomethylpyridine to PbBr