Abstract: We constructed and optimized the plasmid DNA (pDNA) Opt-S encoding the gene of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein, using poly (lactic-co-glycolic acid) copolymer (PLGA) as a delivery carrier for pDNA. PLGA-pDNA NPs were loaded by nanoprecipitation and its properties in vitro were preliminary evaluated. The results showed that the prepared PLGA-pDNA NPs were regular morphology, clear edges, with an average particle size of (184.2 ± 2.4) nm, polydisperse index (PDI) of 0.093 ± 0.013, zeta potential of (-68.10 ± 0.36) mV, and encapsulation rate of (98.92 ± 0.22)%. The PLGA-pDNA NPs were stable at -20 ℃ for 7 months and could protect pDNA against nuclease degradation. And they also exhibited sustained release of pDNA in vitro. The PLGA-pDNA NPs have low cytotoxicity and high safety. In addition, in vitro transfection experiments showed that the SARS-CoV-2 S gene could enter cells and be expressed. These results indicate that PLGA-pDNA NPs non-viral gene vector have simple preparation process and good performance, which are expected to provide a new idea for the research and development of SARS-CoV-2 vaccine.