Fluorescent polydopamine nanoparticles (FPD) are a kind of promising fluorescent nanoparticles for biosensing and imaging, while the rapid and controllable synthesis of FPD is still challenging. In this paper, we developed a microplasma electrochemistry strategy to regulate the oxidative polymerization process of dopamine, resulting in a controlled formation of FPD. Treating the dopamine solution with microplasma anode could not only generate oxidative species to trigger the nucleation of polydopamine nanoparticles at the plasma-liquid interface, but also provide an acidic environment to inhibit their further growing up during the diffusion process. Thus, uniform FPD with a diameter of 3.1 nm could be prepared within minutes. And, continuous generation of FPD could be achieved without the formation of aggregates when prolonging the reaction time. The obtained FPD had abundant functional groups on the surfaces, showing tunable fluorescent emission properties. These luminescent nanoparticles were demonstrated for highly selective detection of uranium with a detection limit of 2.1 mg/L. The novel microplasma electrochemistry strategy established in this work provided better opportunity for controllable synthesis of FPD, as well as other luminescent nanoparticles, and broadened their application in chemical sensing area.