stackpanel本事是提供从上到下跟从做到右的自动填充吧,如果是要从底部排起,可以试用一下dockpanel
<DockPanel HorizontalAlignment="Stretch" VerticalAlignment="Bottom">
<StackPanel Name="stackPanel1" Height="100" DockPanel.Dock="Bottom" />
<StackPanel Name="stackPanel2" DockPanel.Dock="Bottom" Height="100" />
</DockPanel>