<?php

// 替换<p>后4个空格

$str = file_get_contents("http://m.ts.cn/new/99cms_ts/api.php?s=/News/getNewsInfoTmp/Nid/51089");

$str = str_replace(" ", "-", $str);

$str = preg_replace("/\s/", "-", $str);

echo $str;  // 不起作用

<?php

// 替换<p>后4个空格

$str = file_get_contents("http://m.ts.cn/new/99cms_ts/api.php?s=/News/getNewsInfoTmp/Nid/51089");

$str = str_replace(chr(194) . chr(160), "-", $str);  // 解决方法

echo $str;  // OK

<?php

// utf-8无bom文件下，四个空格

$s1 = chr(194) . chr(160);

$s2 = chr(32);

$s3 = " ";

$s4 = "　";  // 全角空格

$s = $s1 . $s2 . $s3 . $s4;

// 判断

$r  = '';

if ($s1 == $s2) $r .= 1;

if ($s1 == $s3) $r .= 2;

if ($s1 == $s4) $r .= 3;

if ($s2 == $s3) $r .= 4;

if ($s2 == $s4) $r .= 5;

if ($s3 == $s4) $r .= 6;

// 结果

echo $s, "#####", $r, "####", str_replace(" ", "-", $s), "####", preg_replace("/\s/", "-", $s);