Private Sub Command3_Click()
   On Error GoTo ErrorHandler
   
    Dim conn As ADODB.Connection
    Dim cmd As
    Dim backupPath As String
   
    ' 设置备份路径
    backupPath = "D:\SQL_Backups\backup_" & Format(Now, "yyyyMMdd_hhmmss") & ".bak"
   
    ' 确保目录存在
    If Dir("D:\SQL_Backups", vbDirectory) = "" Then
        MkDir "D:\SQL_Backups"
    End If
   
    ' 创建连接
    Set conn = New ADODB.Connection
    conn.ConnectionString = "Provider=SQLOLEDB;Data Source=USER-1993088QN;" & _
                          "Initial Catalog=master;User ID=sa;Password=3366489JU;"
    conn.Open
   
    ' 创建命令
    Set cmd = New
    cmd.ActiveConnection = conn
    = "BACKUP DATABASE [管理系统SQL] " & _
                     "TO DISK='" & backupPath & "' " & _
                     "WITH INIT, STATS=10"
    cmd.Execute
   
    MsgBox "备份成功完成! 文件保存在: " & backupPath, vbInformation
   
    Exit Sub
   
ErrorHandler:
    MsgBox "备份失败: " & Err.Description & vbCrLf & _
           "错误号: " & Err.Number, vbCritical
End Sub

首先这个代码只能将数据库备份在数据库所在的服务器上, 也就是你的vb代码也要运行在数据库服务器上
另外要排查问题可以直接在数据库服务器上执行你的backup命令看是否成功