In this study, an effective approach was presented for the synthesis of N-doped carbon dots via a microplasma-assisted process at atmospheric pressure. The effects of operation parameters on the surface groups and photoluminescence (PL) property of carbon dots were studied in detail. Nitrogen element was successfully doped as N–H group and pyrrolic–like structure in the carbon dots. The morphology, structures, chemical compositions and photoluminescence properties of N-doped carbon dots were systematically characterized. The generated chemical species and mechanism were monitored and studied by optical emission spectroscopy. The synthesized particles owned excitation-dependent emission property with a quantum yield up to 9.90%. The plasma treatment time and operating voltage affect the carbonization degree, doping state of nitrogen and particle size, resulting in different PL behaviours. The variation of electrode sizes has slight effects on the yield of N-doped carbon dots from 0.31% to 0.42% owing to the differences in electron density.