使用PHP的字符串替换函数将所有<br /><br />替换为</p><p>。http://php.net/manual/en/function.str-replace.php
样本代码：

$stringWithBRs = nl2br($originalString)
$stringWithPs = str_replace("<br /><br />", "</p>\n<p>", $stringWithBRs);
$stringWithPs = "<p>" . $stringWithPs . "</p>";

或者，您可以使用下面的代码，甚至不调用nl2br（）函数。

$stringWithPs = str_replace("\n\n", "</p>\n<p>", $originalString);
$stringWithPs = "<p>" . $stringWithPs . "</p>";

简单地直接转换原始字符串：

$text=str_replace("<br /><br />", "</p><p>", $original_string);

在HTML中，类似这样的地方：

<p>
 <?php echo $text; ?>
</p>

一句话：

$sNewString = implode('</p><p>',explode('<br /><br />', nl2br($sOriginalString)))

说明：
1.将换行符转换为br
1.通过这些br将字符串拆分为数组
1.通过在每个数组项之间粘贴P标签，将数组粘回到字符串

<?php
   function nl2p($string = '') {
        $array = explode("\n", $string);
        $content = '';
        foreach ($array as $str) {
            $content .= "<p>" . $str . "</p>";
        }
        return $content;
    }

回声nl 2 p（$内容）;

$new = '';
foreach(explode("\n<br /><br />\n", $text) as $p) // split by double newlines
    $new.= "<p>$p</p>\n"; // and convert each part to a paragraph

// or if you want to keep it in a single line
$new = join(array_map(function($p){return "<p>$p</p>\n";}, explode("\n<br /><br />\n", $text)));

"试试看"

$old_string = preg_replace("/[\r\n]/","</p><p>",$old_string);
$new_string = "<p>" . $old_string . "</p>";
echo $new_string;