Ni hao :) It seems that the page you are requesting cannot be decoded properly; in fact if you add the raise_error parameter to decoded_content, you get an error. I used the following test program:

#!/usr/bin/perl

use strict;
use warnings;

use LWP::UserAgent;
use Encode qw/ is_utf8 /;

my $agent = LWP::UserAgent->new();

my @tests = (
  'http://cn.life.dada.net/people/',
  'http://www.sina.com.cn/',
  'http://www.ku6.com/show/34D6sgY4X6w3YegR.html',
  'http://www.xinhua.cn/',
);

foreach my $uri (@tests) {
  eval {
    printf "test: %s\n", $uri;
    my $response = $agent->get($uri);
    my $dc = $response->decoded_content( raise_error => 1 );
    printf "is decoded content utf8? %s\n", is_utf8($dc);
  };

  if ($@) {
    print "decode failed: $@\n";
  }

  print "\n";
}
[download]

You could try to force the charset used by adding charset parameter.