uses
  System.JSON;

procedure TForm1.Button1Click(Sender: TObject);
var
  m_Object, m_Json1, m_Json2: TJSONObject;
  m_JsonArray: TJSONArray;
begin
  m_Object := TJSONObject.Create;
  try
    // JSON数组
    m_JsonArray := TJSONArray.Create;
    // 数组成员一
    m_Json1 := TJSONObject.Create;
    m_Json1.AddPair('姓名', TJSONString.Create('张三'));
    m_Json1.AddPair('成绩', TJSONNumber.Create(75.5));
    m_JsonArray.Add(m_Json1);
    // 数组成员二
    m_Json2 := TJSONObject.Create;
    m_Json2.AddPair('姓名', TJSONString.Create('李四'));
    m_Json2.AddPair('成绩', TJSONNumber.Create(21.7));
    m_JsonArray.Add(m_Json2);
    // JSON对象
    m_Object.AddPair('五班', m_JsonArray);
    // 输出
    Memo1.Lines.Clear;
    Memo1.Lines.Add(m_Object.ToString);
  finally
    m_Object.Free;
  end;
end;