why the ranking of website is different in different countries?

[PpcJen]

Google give preference to local sites hosted on local servers.

So if you have a site based in the UK, and all things are equal, your site will get preference to viewers in the UK.

[aussieroo1]

What exactly do you mean? If you are talking about the search engines, (google.com and google.com.au for example), I guess it depends on the competitiveness of your website to other companies in your particular industry. I'm not sure if I answered your question though.

[PpcJen]

The pages above you in the UK may be hosted on UK servers or they may be something.co.uk - which gives them preference.