Hi sallmomar,

Check this example. Now please take its reference and correct your code.

Database

CREATE TABLE [Site]
(
	Id INT PRIMARY KEY IDENTITY,
	Nom VARCHAR(10),
	Marque INT,
	Model VARCHAR(10),
	Numero VARCHAR(10),
	Plage VARCHAR(10)
)
GO
INSERT INTO [Site] VALUES('Nom1', 1, 'fa', 'duo', 'lo')
INSERT INTO [Site] VALUES('Nom1', 2, 'fi', 'da', 'lle')
INSERT INTO [Site] VALUES('Nom1', 3, 'fa', 'di', 'llww')
INSERT INTO [Site] VALUES('Nom2', 4, 'fa', 'du', 'lo')
INSERT INTO [Site] VALUES('Nom2', 5, 'fi', 'da', 'lle')
INSERT INTO [Site] VALUES('Nom3', 6, 'fa', 'di', 'llww')

Controller

public class HomeController : Controller
{
    // GET: /Home/
    public ActionResult Index()
    {
        TestEntities db = new TestEntities();
        TempData["listesite"] = db.Sites.ToList();
        return View();
    }
}

View

<table>
    <tr>
        <th>Nom</th>
        <th>Marque</th>
        <th>Model</th>
        <th>Nuemro</th>
        <th>Plage</th>
    </tr>
    <%foreach (var item in ((List<Site>)TempData["listesite"]).GroupBy(x => x.Nom))
        {%>
    <tr>
        <th><%=item.Key %></th>
        <th colspan="4"></th>
    </tr>
    <%foreach (Site data in ((List<Site>)TempData["listesite"]).Where(x => x.Nom == item.Key))
        {%>
    <tr>
        <td></td>
        <td><%=data.Marque%></td>
        <td><%=data.Model%></td>
        <td><%=data.Numero%></td>
        <td><%=data.Plage%></td>
    </tr>
    <% } %>
    <%} %>
</table>

Screenshot