The effects of nano- zinc citrate (NZnC) on the foaming behaviors of polylactic acid(PLA) were investigated in continuous extrusion foaming with supercritical CO₂ as blowing agent. First, the effects of five nucleating agents (nano zinc citrate(NZnC), food grade zinc citrate(FZnC), nano silica(N-SiO₂), diphenyl sebacic acid dihydrazide(TMC-300) and talc) on the isothermal crystallization behavior of PLA, micro-morphologies of nucleating agent/PLA composites, foaming performance and compression performance of PLA foam were studied by differentialscanning calorimeter(DSC), scanning electron microscope(SEM) and compression testing machine. The results show that NZnC has the fastest isothermal crystallization rate of PLA, the best dispersibility and compatibility in PLA, and the best modification effect of foaming performance and compression performance of PLA foam. And then, the effects of NZnC content on the foaming performance and compression performance of PLA foam were studied. The results show that when the NZnC mass fraction is 0.5%, the PLA foam has the best foaming performance (the foaming ratio is 31 times, the cell density is 3.02×10⁹ cm- 3, and the average cell diameter is 17.11 μm), and the compression performance is also the best (the compressive modulus is 19 MPa, the compressive strength is 0.35 MPa).