how to give read more link in a block? I have a views block which display user's detail like name, picture and about.
i want to give a read more link in "about" field, by click "read more" link the trimmed "about" will open in the same block.

"About" is a field from view, so in this field text will trim after 200 words if the about field is more then 200 words then after trimmed part there will be a read more link and after clicking this link the whole text will visible on the same position just increase the height of the block. 

Thanks
jQuery expander module will work for you.

You will have to select expander from formater options in views field configuration.