Nickel-titanium alloy (NiTi alloy) has recently received an increasing amount of attention. However, the release of toxic nickel ions and the threat of implant infections has limited its clinical applications. Thus, we report a promising copolymer coating with excellent nickel ion (Ni²⁺) inhibition release, cytocompatibility, and antimicrobial properties to solve these safety issues involving NiTi alloy implantation. Quaternized copolymers poly (7-hydroxy-4-methylcoumarin methacrylate-co-2-hydroxyethyl methacrylate-co-2-(dimethylamino)ethyl methacrylate) (PCHD-Q) with many hydroxyl and tertiary amine groups were first synthesized, self-assembled into nanoparticles, and then deposited on NiTi substrate through electrodeposition. After UV irradiation, scanning electron microscopy (SEM) images revealed that homogeneous, continuous, and dense coatings were obtained. The coatings showed good improvement of protective behavior for the NiTi alloy in an in vitro environment and could significantly decrease the release of Ni²⁺ through physical barriers and physical adsorption, which could obviously reduce cytotoxicity inducing by Ni²⁺. According to in vitro cell viability and antibacterial tests, the quaternized coating materials not only provided a relatively stable biointerface for cell adhesion, spreading and growth, but also obtained excellent antimicrobial activity for the bare NiTi alloy against S. aureus and E. coli. These results suggested that our coatings materials have the potential for improving the safety and success rate of NiTi-based implantations.