可以使用Dictionary对象为每一列存储“禁用”数字

Option Explicit

Public Sub generateRandNum()
    'Define your variabiles
    Dim lowerbound  As Long, _
        upperbound  As Long
    lowerbound = 1
    upperbound = 20 '20000
    
    
    'define forbidden numbers for each single column
    Dim forbiddenNumbersDict As Object
        Set forbiddenNumbersDict = CreateObject("Scripting.Dictionary")
            With forbiddenNumbersDict
                .Add 2, Array(1, 4, 9) ' column 2 forbidden numbers
                .Add 3, Array(2, 5, 7) ' column 3 forbidden numbers
                '....
            End With
    
    Dim randomrange As Range
    Set randomrange = Range("A1:C5")
    randomrange.Clear
    
    Dim counter As Long
        counter = randomrange.Count
    
    If counter > upperbound - lowerbound + 1 Then
        MsgBox ("Number of cells > number of unique random numbers")
        Exit Sub
    End If
    
    Dim rng As Range
    For Each rng In randomrange
    
        Dim rngColIndex As Long
            rngColIndex = rng.Column ' locate the current column
            
        Dim randnum As Long
        randnum = Int((upperbound - lowerbound + 1) * Rnd + lowerbound)
            Do While Application.WorksheetFunction.CountIf(randomrange, randnum) >= 1 _
                     Or Not IsError(Application.Match(randnum, forbiddenNumbersDict(rngColIndex), 0)) ' added the condition to exclude forbidden numbers for the current column
                randnum = Int((upperbound - lowerbound + 1) * Rnd + lowerbound)
            Loop
                rng.Value = randnum
    Next
End Sub

顺便说一句，你的算法效率很低