if i have a page and the url of the page is crawled by google. but when a user click on the link in SERP, link redirect user to another page. how can it possible please help me.
I agree with laptop, it is likely your domain has been hijacked. Any more info about the type of redirect?
URL Masking means that the visitors to the domain name will be forwarded to your destination website, however the URL in their browser address bar will remain the same. In case of URL Masking the Domain Forwarding server sends the client a Frames page where the Frame Source contains the destination URL you have specified. This ensures that the URL in the address bar of the browser does not change though the client sees the destination page.
yes your site is in danger. If it is redirected and you are not aware of it, then quickly change your password. Or complain your domain provider