The cell nucleation and cell growth of microcellular foaming in supercritical CO2 pressure quench process was investigated by means of dual depressurization and cooling Cyclic Olefin Copolymer (COC) was saturated under supercritical CO2 circumstance

and then the system was depmssurized to an intermediate pressure．After that

four methods of re-depressurization and cooling were adopted．Several novel cell structures were prepared in this way

such as cells with transitional layers and bimodal-size-distribution cens．It was found that most of the nuclei disappear or coalesce during cell growth process with only a small fraction growing to stable cells

and the final cell structure strongly depends on the cell growth process．Dual nucleation occurs only in a certain depressurization range．Final cell structures obtained in dual depressurization are closely correlative to the solubility variation of CO2 under corresponding pressures．