$d = new Datetime("2015-03-02 18:00:00");
echo $d->modify("-1 day")->format("Y-m-d H:i:s");

$date = new DateTime('2015-02-14');
$diff = new DateInterval('P1D');
$date->sub($diff);

echo $date->format('Y-m-d'); // 2015-02-13

获取的某一天肯定是已知的，直接手动设置成已知时间减去一天的时间就好了吧

<?php 
    echo (new DateTime("2014-10-25 -1 days", new DateTimeZone("Asia/Shanghai")))->format("Y/m/d"), "\r\n";

    // or 

    echo date("Y-m-d", strtotime("2014-10-25 -1 days")), "\r\n";
?>

date('Y-m-d',strtotime($date.'-1 day'))

把指定$date传入就行了