Rockmass classification Q system, which has been widely used in many countries, was firstly presented by Barton in 1974. It has been one of the most popular rockmass classification systems in the world. The support design based on Q system of 2002 edition is introduced in summary, the applicability of the Q system in an underground oilstorage cavern is testified, and reasonable explanation for detailed parameter selection is given In the beginning of the project, both RMR system and Q system are used, the correlation between Q system and RMR system is established and the rock mass standup time is determined on basis of RMR system It is proposed that experienced geological engineer should make evaluation on the rock mass quality on the site, in order to ensure the validity of the application of Q system.