'add a textbox with "multiline=true","scrollbars=2".

Private Declare Function SendMessage Lib "USER32" Alias "SendMessageA" _
    (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, _
    lParam As Any) As Long
Private Declare Function SendMessageByNum Lib "USER32" _
    Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, _
    ByVal wParam As Long, ByVal lParam As Long) As Long
Private Declare Function SendMessageByString Lib "USER32" Alias _
    "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam _
     As Long, ByVal lParam As String) As Long

Private Const EM_LINEINDEX = &HBB
Private Const EM_GETLINECOUNT = &HBA
Private Const EM_GETLINE = &HC4
Private Const EM_LINELENGTH = &HC1

Function GetLineText(ByVal txtbox As TextBox, ByVal LineIndex As Long) As String '返回指定行的内容
  Dim lc As Long, linechar As Long
  linechar = SendMessageByNum(txtbox.hWnd, EM_LINEINDEX, LineIndex, 0)
  lc = SendMessageByNum(txtbox.hWnd, EM_LINELENGTH, linechar, 0) + 1
  GetLineText = String(lc + 2, 0)
  Mid(GetLineText, 1, 1) = Chr(lc And &HFF)
  Mid(GetLineText, 2, 1) = Chr(lc \ &H100)
  lc = SendMessageByString(txtbox.hWnd, EM_GETLINE, LineIndex, GetLineText)
  GetLineText = Left(GetLineText, lc)
End Function

Function getlinewithstr(ByVal txtbox As TextBox, ByVal mystr As String) As String
Dim linecount As Long, temp() As String, i As Long
linecount = SendMessage(txtbox.hWnd, EM_GETLINECOUNT, 0, 0) '返回行数
ReDim temp(1 To linecount)
For i = 1 To linecount
temp(i) = "第" & i & "行：" & GetLineText(txtbox, i - 1) '添加行号
Next
getlinewithstr = Join(Filter(temp, mystr), vbCrLf) ' 字符串过滤
Erase temp
End Function

Private Sub Command1_Click()
MsgBox getlinewithstr(Text1, "CSDN"), 0, "包含“CSDN”的行"
End Sub

Private Sub Form_Load()
Dim a(25) As String, i As Long
For i = 0 To 25
a(i) = String(50, Chr(i + 97))
Next
Text1.Text = Join(a, "CSDN")

End Sub