Picture1.Print Chr(j + 64) & "=" & "a(j)";中a(j)是不要加“”的，否則就變成了字串了，還有在picturebox裡列印時最好換行，不要列印在一行上，太長了，所以，建議你把後面冒號也去掉，如下：

Private Sub Command1_Click()

Dim c As String, x%, a(1 To 26) As Integer

For i = 1 To Len(Text1.Text)

c = UCase(Mid(Text1.Text, i, 1))

If c >= "A" And c <= "Z" Then

j = Asc(c) - 64

a(j) = a(j) + 1

End If

Next i

For j = 1 To 26

Picture1.Print Chr(j + 64) & "=" & a(j)

Next j

End Sub