var row = [{ "code": "1", "model": "APOLLO" }, { "code": "2", "model": "APOLLO M/B1"}];
for (var i = 0; i < row.length; i++) {
var addOption = document.createElement("option");
addOption.text = row[i]["model"];
addOption.value = row[i]["model"];
document.getElementById("ddlModel").add(addOption);
}

<asp:DropDownList ID="ddlModel" name="ddlModel" runat="server" Font-Size="9pt" Width="105px"
CssClass="DropDownList">
</asp:DropDownList>