How can i create html pages dynamically in asp.net

Double click the button in the designer, and it will generate an event handler for you. Then put your code to add the dymanic html in the handler.

If you are worried about how to insert the HTML then one method is to add an ASP.NET Literal control to the postion in the page you want to generate the HTML, then set its Text property to the HTML you have generated.

You could also override to the page's Render method an use it to write the HTML to the client. You'd need to check the page is under postback (and, optionally, that the button has been clicked depending upon your needs). The other thing to do is not to call the base Render method, as is sometimes done when overriding it.

Finally, I'd suggest you think about whether your strategy is appropiate (it could be-but it doesn't harm to examine what you are doing). For example it is normally better to dynamically add ASP.NET controls to the page, or create a control that renders the html you want. If you need really fine control over the HTML across most of your application MVC3 might be a better choice.