Private Sub Command1_Click()
Dim marc As AcadArc
Dim mcen(2) As Double
Dim mr As Double
Dim mstaga As Double
Dim menag As Double

mcen(0) = Val(Text1.Text)
mcen(1) = Val(Text2.Text)
mcen(2) = Val(Text3.Text)
mr = Val(Text4.Text)
mstag = Val(Text5.Text) * 3.1415926 / 180
menag = Val(Text6.Text) * 3.1415926 / 180

（此行显黄）Set marc = acaddoc.ModelSpace.AddArc(mcen, mr, mstag, menag)

marc.Update
ZoomAll
End Sub

肯定是这行出问题了   Set marc = acaddoc.ModelSpace.AddArc(mcen, mr, mstag, menag)
一般424错误是对象引用不正确，或对象属性有错误，由于不知道你的具体的对象设置，无非具体回答。