00Cr12Ni9Mo4Cu2　is　an　ultra-　high　strength,　maraging　stainless　steel.　Optical　microscopy,　microhardness　measurement,　scanning　electron　microscopy　(SEM),　and　transmission　electronic　microscopy　(TEM)　were　used　to　quantitatively　investigate　the　effect　of　the　solid　solution　parameters　on　the　grain　size　and　the　secondary　phases　of　the　steel.　It　was　found　that　the　grain　size　increased　from　8.5　um　to　28　um　when　the　solid　solution　temperature　was　increased　from　960　degrees　C　to　1040　degrees　C.　Meanwhile,　the　strength　of　the　alloy　increased　from　822　MPa　to　1054　MPa.　However,　when　the　temperature　was　increased　from　1040　degrees　C　to　1100　degrees　C,　the　grain　size　rose　dramatically　to　55　um,　and　the　strength　of　the　alloy　decreased　from　1054　MPa　to　782　MPa.　Most　of　the　original　carbides　were　dissolved　when　the　solid　solution　temperature　increased　up　to　1040　degrees　C.　Finally,　a　constitutive　equation　based　on　the　evolution　of　the　subgrain　size　is　proposed,　clarifying　the　relationship　between　the　mechanical　properties　and　microstructures.