Abstract: Magnetite nanoparticles (MNPs) are widely utilized for heavy metal adsorption, organic pollutant degradation and water remediation due to their large specific surface area, high reactivity, and facile magnetic separation. However, pure MNPs tend to aggregate rapidly in aquatic environments, which reduces their accessible surface area and active sites, decreases mobility, and ultimately limits remediation efficiency. Surface organic coating is an effective strategy to enhance the colloidal stability of MNPs, nevertheless, the diversity of coating types and the complexity of environmental factors mean that the underlying regulatory mechanisms remain insufficiently clarified. The effects of small organic acids, polymeric ligands, and surfactants on the stability of MNPs are summarized in this review. Small organic acids, such as acetic acid (AA), citric acid (CA), and oleic acid (OA), regulate surface charge via –COOH/–OH groups, typically shifting the zeta potential (ζ) from approximately −20 mV to a range of –35 to –30 mV, thereby strengthening electrostatic repulsion. Polymeric coatings, including poly (acrylic acid) (PAA), polyethylene glycol (PEG), and carboxymethyl cellulose (CMC), form 5−20 nm steric layers, maintain |ζ| at 30−40 mV, and ensure superior dispersion under high salinity and across a broad pH range. For instance, CMC coated MNPs exhibit hydrodynamic diameters of 40−120 nm and the adsorption capacity of a Pb²⁺ was 152 mg/g, demonstrating excellent environmental robustness. Environmental pH, ionic strength, ion valence, and natural organic matter (NOM) are identified as primary factors controlling the stability of organic-coated MNPs. Specifically, NOM adsorption, which is typically 50−250 times higher than that of the original organic coating, can reconfigure surface chemistry and aggregation pathways. Additionally, light, oxidative ageing, and microbial processes may decompose or reconstruct coatings, shifting aggregation mechanisms between suppression and promotion. Evidence from DLVO/EDLVO analysis, combined with dynamic light scattering (DLS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), demonstrates that MNP aggregation is governed by the coupled effects of electrostatic repulsion, steric repulsion, cation bridging, and patch-charge attraction, with the dominant interaction shifting in response to environmental conditions. A mechanistic understanding of the co-regulation by organic coatings and environmental factors provides a theoretical basis for designing highly stable and environment-friendly MNP-based remediation materials. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202507160204.