Monodispersed magnetic sorbents (MMSs) display great potential for adsorptive removal of pollutants, but the conventional methods cannot meet requirements of scalable, time-saving, and energy-efficient fabrication. In this work, space-confined synthesis of nitrilotriacetic acid immobilized magnetic sorbents (NAIMSs-E) in aqueous continuous phase of high internal phase emulsions (HIPEs) was conducted, and as-prepared high quality sorbents (sensitive response to magnetic field, abundant affinity groups, uniform shell size, and stable structure) were applied for removing bivalent cadmium (Cd²⁺) from aqueous solutions. 2-(Bis-carboxymethyl-amino)-6-{3-[2-(3,4-dihydroxy-phenyl)-ethylcarbamoyl]-propionylamino}-hexanoic acid was firstly synthesized as a robust anchor and a functional modifier onto magnetic Fe₃O₄. The effects of synthesis conditions to the morphology and structure were studied, and the forming mechanism based on emulsion nano-reactor was demonstrated. NAIMSs-E are expected to possess fast equilibrium rate, and approximately 90% of the maximum adsorption capacity is achieved within 60 min. The maximum uptake amounts are 49.98 mg g^-1, 80.58 mg g^-1, 176.4 mg g^-1 at 288 K, 298 K, and 308 K, respectively, and the monolayer chemisorption based on sharing and transferring of electrons is the main rate-limiting step. Moreover, NAIMSs-E have excellent regeneration and specific affinity towards Cd²⁺, even for actual water samples. In addition, the spontaneous, endothermic, and entropy increased adsorption process is also confirmed. Therefore, this work not only presents a new clue to fabricate MMSs via simple emulsion nano-reactor, but also provides a novel platform for Cd²⁺ removal.