$days = array('日','一','二','三','四','五','六');

$today = date('w')-1;

$this_monday = strtotime('-'.$today.' day');

echo "今天是：星期",$days[$today],"

本周一：",date('Y-m-d',$this_monday),"

下周一：",date('Y-m-d',strtotime('+1 week',$this_monday));

?>