I am new in blockchain. I want to know that which database should I use to store blockchain data? How can i store blockchain data in codeigniter?
You cannot store data in CodeIgniter, as it is a MVC PHP framework to write web applications. It is no kind of data storage of any kind at all; it may just allow you to connect to one.
In case you want to write an application in CodeIgniter which will allow you to view and possibly edit blockchain data, then you would indeed either have to copy the blockchain data into a database which is supported by CodeIgniter out of the box (IIUC, LevelDB isn't one of them) or you will have to figure out how to connect CodeIgniter to LevelDB.
Given the fact that all databases which are mentioned in the CodeIgniter documentation are relational databases, your milage may vary.