最简单的是先做base64编码，然后不存在什么中文的问题了，再xor下。解密相反，先xor，然后base64解码
如果要完整代码，请先采纳下。

 Option Explicit
Private Const cstBase64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
Private arrBase64() As String

Public Function 加密(strSource As String, key As String) As String
    On Error Resume Next
    If UBound(arrBase64) = -1 Then
        arrBase64 = Split(StrConv(cstBase64, vbUnicode), vbNullChar)
    End If
    Dim arrB() As Byte, bTmp(2) As Byte, bT As Byte
    Dim I As Long, J As Long
    arrB = StrConv(strSource, vbFromUnicode)

    J = UBound(arrB)
    For I = 0 To J Step 3
        Erase bTmp
        bTmp(0) = arrB(I + 0) Xor (Asc(Mid(key, I \ 3 Mod Len(key) + 1, 1)) Mod 256)
        bTmp(1) = arrB(I + 1) Xor (Asc(Mid(key, I \ 3 Mod Len(key) + 1, 1)) Mod 256)
        bTmp(2) = arrB(I + 2) Xor (Asc(Mid(key, I \ 3 Mod Len(key) + 1, 1)) Mod 256)

        bT = (bTmp(0) And 252) / 4
        加密 = 加密 & arrBase64(bT)

        bT = (bTmp(0) And 3) * 16
        bT = bT + bTmp(1) \ 16
        加密 = 加密 & arrBase64(bT)

        bT = (bTmp(1) And 15) * 4
        bT = bT + bTmp(2) \ 64
        If I + 1 <= J Then
            加密 = 加密 & arrBase64(bT)
        Else
            加密 = 加密 & "="
        End If

        bT = bTmp(2) And 63
        If I + 2 <= J Then
            加密 = 加密 & arrBase64(bT)
        Else
            加密 = 加密 & "="
        End If
    Next
End Function

Public Function 解密(strEncoded As String, key As String) As String
    On Error Resume Next
    Dim arrB() As Byte, bTmp(3) As Byte, bT As Long, bRet() As Byte
    Dim I As Long, J As Long
    arrB = StrConv(strEncoded, vbFromUnicode)
    J = InStr(strEncoded & "=", "=") - 2
    ReDim bRet(J - J \ 4 - 1)
    For I = 0 To J Step 4
        Erase bTmp
        bTmp(0) = ((InStr(cstBase64, Chr(arrB(I))) - 1) And 63)
        bTmp(1) = ((InStr(cstBase64, Chr(arrB(I + 1))) - 1) And 63)
        bTmp(2) = ((InStr(cstBase64, Chr(arrB(I + 2))) - 1) And 63)
        bTmp(3) = ((InStr(cstBase64, Chr(arrB(I + 3))) - 1) And 63)

        bT = bTmp(0) * 2 ^ 18 + bTmp(1) * 2 ^ 12 + bTmp(2) * 2 ^ 6 + bTmp(3)

        bRet((I \ 4) * 3) = (bT \ 65536) Xor (Asc(Mid(key, I \ 3 Mod Len(key) + 1, 1)) Mod 256)
        bRet((I \ 4) * 3 + 1) = ((bT And 65280) \ 256) Xor (Asc(Mid(key, I \ 3 Mod Len(key) + 1, 1)) Mod 256)
        bRet((I \ 4) * 3 + 2) = (bT And 255) Xor (Asc(Mid(key, I \ 3 Mod Len(key) + 1, 1)) Mod 256)
    Next
    解密 = StrConv(bRet, vbUnicode)
End Function

Private Sub Command1_Click()
    Text3.Text = 加密(Text2.Text, Text1.Text)
End Sub

Private Sub Command2_Click()
    Text2.Text = 解密(Text3.Text, Text1.Text)
End Sub

看的不是怎么太清楚。。。