In my project i have to create an Accordion.which is better to use Jquery or Ajax
AJAX is for server-side requests, to get or send new data for your page (without a full page reload), it's an alltogether different concept.
For the accordion, I think you're looking for the jQuery UI accordion, though there are many options out there.
AJAX, or Asynchronous Javascript and XML, is an umbrella term for the technologies and methodologies involved in loading data from the server without a page request.
jQuery is a Javascript library.
Javascript is a client side scripting language.
As @Nick said, the jQuery UI accordion plugin is a good choice for the accordion.
See this accordion made with jquery:
http://sarfraznawaz.wordpress.com/2010/03/09/creating-stylish-sliding-menu-with-jquery/
That's a bit like asking "What should I use to get to work today? A car or an accelerator pedal?"
AJAX is a general term that refers to the techniques that make use of client-side scripting (e.g. JavaScript) to communicate with the server between page-loads.
jQuery is a framework (a set of libraries and tools) that make writing JavaScript simpler and easier. It includes facilities for using AJAX.