....
<myCtrl:PicUpload ID="fileUpload1" runat ="server" TargetFolder ="~/Docs/" FilePrefix ="doc" />
<br />
<asp:Button ID="btnMore" runat ="server" Text ="添加更多控件" />
<br />
<asp:Panel ID ="panelSpec" runat ="server" >
</asp:Panel>
....

Shared ctrlUploadList As New List(Of UserControl_PicUpload)
Shared ctrlID As Integer = 2   '目标页面中已经存在了一个同样的控件，ID为1，动态加载的控件ID从2开始

Protected Sub btnMore_Click(sender As Object, e As System.EventArgs) Handles btnMore.Click

        'PicUpload为控件名称，放在UserControl文件夹内
        Dim newFileUpload = New UserControl_PicUpload() With { _
            .ID = "fileUpload" & ctrlID.ToString, _
            .FilePrefix = "doc", _
            .TargetFolder = "~/Docs/"}
        
        'panelSpec是一个panel控件的ID，用来存放动态加载的控件
        panelSpec.Controls.Add(newFileUpload)
        ctrlUploadList.Add(newFileUpload)
        ctrlID += 1
End Sub

'通过RestoreControls避免丢掉之前动态加载的控件
Protected Sub RestoreControls()
        Dim myfileUpload As UserControl_PicUpload

        For Each myfileUpload In ctrlUploadList
            If myfileUpload IsNot Nothing Then
                panelSpec.Controls.Add(myfileUpload)
            End If
        Next
End Sub

Protected Sub Page_Load(sender As Object, e As System.EventArgs) Handles Me.Load
        If Not IsPostBack Then
        ... '页面加载时对其他控件进行初始化
        End If

        RestoreControls()
End Sub

AddProValue apv = (AddProValue)Page.LoadControl("UserControl/AddProValue.ascx");
                apv.Num = Convert.ToInt32(kvp.Key);
                apv.ProValue = kvp.Value;
                apv.ID = "apv" + Convert.ToString(kvp.Key);
                this.ph1.Controls.Add(apv);

------解决方案--------------------
你可以直接写空间， 也可以继承某个控件， 然后编译成dll，   项目引用改dll