Get Subtype of featureclass using arcobject.
IWorkspaceFactory pworkspacefactory = new FileGDBWorkspaceFactoryClass();
IWorkspace pworkspace = pworkspacefactory.OpenFromFile(@"C:\temp\temp1\Data.gdb", 0);
IFeatureWorkspace pfeatureworkspace = pworkspace as IFeatureWorkspace;
IFeatureClass pFeatureclass = pfeatureworkspace.OpenFeatureClass("Manmade_Features");
FCAliasName = pFeatureclass.AliasName;
FCType = pFeatureclass.ShapeType.ToString();
FCShpFldName = pFeatureclass.ShapeFieldName;
IDataset pDataSet = pFeatureclass as IDataset;
FCName = pDataSet.Name;
ISubtypes psubtype = pFeatureclass as ISubtypes;
IEnumSubtype penumSubtypes = psubtype.Subtypes;
int subTypeCode=0;
String codVal= penumSubtypes.Next(out subTypeCode);
while (codVal != null)
{
SubtypeCodeVal[subTypeCode] = codVal;
codVal = penumSubtypes.Next(out subTypeCode);
}