How to load the required modules only on Drupal site? I have a site which contains more than 100 modules. So, for each page every module is getting loaded. 

Is there any way to load only required modules to that particular page?
No, there's no such way. Or may be answer is: Yes, it's done automatically. Keep in mind that Drupal loads only the .module file always, and other files (includes, classes, etc) are only loaded when needed. Is true that that 'when needed' may be always for some of the files, but not all.