I found that promote my website on internet is very difficult to me,so I want to
buy traffic for sale,Is there some companys can offer such service?
I would suggest taking a look at something like Google adwords, but there are a few things you can do, SEO, also ensure your listed with all the search engines, with good tags, not just Google.
You can do banner advertising, blog advertising....the sky is the limit when driving traffic, but it all comes at a cost!