Vb6调用C#生成的dll

namespace ClassLibrary1
{
    [ClassInterface(ClassInterfaceType.AutoDispatch)]     //注意这行，这行是关键
    public class Class1
    {
        public int add(int a, int b)
        {
            return (a + b);
        }

    }
}

Option Explicit

Private Sub Command1_Click()
    Dim obj As Object
    Set obj = CreateObject("ClassLibrary1.Class1")

    Dim iRnt As Integer
    iRnt = obj.Add(2, 3)

    MsgBox iRnt
End Sub

参考：https://blog.csdn.net/hrex/article/details/6936201