Hi Manal,
Please elaborate on this question. The following code shows how to create a chart with two high low series:

   NCartesianChart chart = (NCartesianChart)nChartControl1.Charts[0];
   
   // set a chart title
   NLabel title = nChartControl1.Labels.AddHeader("2D High Low Chart");
   title.TextStyle.FontStyle = new NFontStyle("Times New Roman", 18, FontStyle.Italic);
   title.TextStyle.FillStyle = new NColorFillStyle(Color.Gray);

   // add a High-Low series
   Random rand = new Random();
   
   NHighLowSeries highLow1 = (NHighLowSeries)chart.Series.Add(SeriesType.HighLow);
   highLow1.Name = "High-Low 1";
   highLow1.HighFillStyle = new NColorFillStyle(Color.Gray);
   highLow1.LowFillStyle = new NColorFillStyle(Color.DarkOrange);
   highLow1.DataLabelStyle.Visible = false;

   highLow1.ClearDataPoints();

    
   for (int i = 0; i < 20; i++)
   {
    double d1 = Math.Log(i + 1) + 0.1 * rand.NextDouble();
    double d2 = d1 + Math.Cos(0.33 * i) + 0.1 * rand.NextDouble();

    highLow1.HighValues.Add(d1);
    highLow1.LowValues.Add(d2);
   }

   // add a High-Low series
   NHighLowSeries highLow2 = (NHighLowSeries)chart.Series.Add(SeriesType.HighLow);
   highLow2.Name = "High-Low 2";
   highLow2.HighFillStyle = new NColorFillStyle(Color.Red);
   highLow2.LowFillStyle = new NColorFillStyle(Color.Green);
   highLow2.DataLabelStyle.Visible = false;

   highLow2.ClearDataPoints();

   for (int i = 0; i < 20; i++)
   {
    double d1 = Math.Log(i + 1) + 0.5 * rand.NextDouble();
    double d2 = d1 + Math.Cos(0.33 * i) + 0.5 * rand.NextDouble();

    highLow2.HighValues.Add(d1);
    highLow2.LowValues.Add(d2);
   }

Generally you can mix an unlimited number of series in a chart.