i am use
SAPbobsCOM.UserFieldsMD FieldsMD;
FieldsMD = (SAPbobsCOM.UserFieldsMD)oCompany.GetBusinessObject(SAPbobsCOM.BoObjectTypes.oUserFields);
if (!ClsDIGeneric.DoesUserFieldExist(oCompany, "ORDR", "INSP"))
{
FieldsMD.TableName = "ORDR";
ClsDIGeneric.AddUserField(oCompany, FieldsMD, "INSP", "inspct", SAPbobsCOM.BoFieldTypes.db_Alpha, SAPbobsCOM.BoFldSubTypes.st_None, 100, "", SAPbobsCOM.BoYesNoEnum.tNO);
}
System.Runtime.InteropServices.Marshal.ReleaseComObject(FieldsMD);
Code For Add Column In System table.