How to increase a space between two lines in multiline label ??
Short answer: you can't. To change the spacing between lines of text, you will have to subclass UILabel and roll your own drawTextInRect, or create multiple labels.
Long answer: In the print and online world, the space between lines of text is known as "leading." Leading is a read-only property of UIFont, which was deprecated in 4.0 and replaced by lineHeight. As far as I know, there's no way to create a font with a specific set of parameters such as lineHeight; you get the system fonts and that's it.
There is no spacing parameter in UILabel, either.
I'm not particularly happy with UILabel's behavior as is, so I suggest writing your own subclass. That will make the behavior independent of your font choice and be the most reusable solution.
I wish there was more flexibility in UILabel, and I'd be happy to be proven wrong!