The documents for applying a multi-entry visa are:
your financial capability of covering the travelling expenses in China; your passport with blank pages and at least 6 months validity left before expiration; a truly and completely filled application form affixed with one passport-sized photo and other documents required by the visa officers if necessary.
For the detailed and exact info., please contact the Chinese embassy in Nigeria, whose official website is
http://sy.chineseembassy.org/eng/