After 2 hours of looking for help from different documentation & sites, I found out none of them are complete solution. So, I summary my instruction here:
1) yum install php-devel
2) cd /usr
3) wget http://pear.php.net/go-pear
4) php go-pear
5) See the following line in /etc/php.ini [include_path=".:/usr/PEAR"]
6) pecl install imagick
7) Add the following line in /etc/php.ini [extension=imagick.so]
8) service httpd restart
Hopefully, I can save other engineer effort & time.... Good luck!