图中的两条红线的标注尺寸怎么获得呢？

可以通过XY轴判断
Function GetDimByX(ByVal X)
'获取一标注点的横坐标为X的所有标注
       Dim FilterType(6) As Integer
       Dim FilterData(6) As Variant
       Dim pDims() As AcadObject
       Dim ss As AcadSelectionSet
       Dim pnt(2) As Double
       pnt(0) = X
       FilterType(0) = 0
       FilterData(0) = "Dim*"
       FilterType(1) = -4
       FilterData(1) = ""
       Set ss = ThisDrawing.ActiveSelectionSet
       ss.Clear
       ss.Select acSelectionSetAll, , , FilterType, FilterData
       ReDim pDims(ss.Count - 1)
       For i = 0 To ss.Count - 1
               Set pDims(i) = ss(i)
       Next i
       GetDimByX = pDims
End FunctionFunction GetDimByY(ByVal Y)
'获取一标注点的纵坐标为Y的所有标注
       Dim FilterType(6) As Integer
       Dim FilterData(6) As Variant
       Dim pDims() As AcadObject
       Dim ss As AcadSelectionSet
       Dim pnt(2) As Double
       pnt(1) = Y
       FilterType(0) = 0
       FilterData(0) = "Dim*"
       FilterType(1) = -4
       FilterData(1) = ""
       Set ss = ThisDrawing.ActiveSelectionSet
       ss.Clear
       ss.Select acSelectionSetAll, , , FilterType, FilterData
       ReDim pDims(ss.Count - 1)
       For i = 0 To ss.Count - 1
               Set pDims(i) = ss(i)
       Next i
       GetDimByY = pDims
End FunctionSub Test2()
Dim obj As AcadLine
ThisDrawing.Utility.GetEntity obj, pnt
Dim a As Double
a = obj.StartPoint(0)
For Each i In GetDimByX(a)
MsgBox i.ObjectName
Next i
End Sub