I am making a simple struts application in which if i use only one input text box then this application is running very well but as if i increses thje input box no by 2 then i get HTTP error 500, wheather i've make changes in action class and bean class.

In a struts application every element in JSP that will hold some value should be defined in the Form bean class. So if you are declaring 2 text boxes in your JSP you need to have 2 form bean elements in your Form bean class. For eg :if your JSP has two text boxes 1 for username & anotyher for password than you form bean should have two String variables userName and passowrd and the getter and setter for both the elements.
And according you can get the values of your form bean elements in your Action class.