[System.reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint")

$siteUrl = "SPS Server URL"

$webName = "SubSite"

$listName = "List Name"

$site=Get-SPSite($siteUrl)

$web=$site.openweb($webName)

$list=$web.Lists[$listName]

$items=$list.Items

Write-Host  $items.Count  

$items|%{$list.GetItemById($_.Id).Delete()}  

$web.Dispose()

$site.Dispose()