If you need invitation letter for visa application, please contact our conference secretary: Yepang Liu (firstname.lastname@example.org).
The HongKong Immigration Department's webpage contains details on visas.
Hong Kong Special Administrative Region:
Many foreign nationals do not require a visa to visit Hong Kong, providing they have a passport that is valid for a minimum of 6 months--their stay is usually limited to 90 days.
More information about visas: http://www.immd.gov.hk/en/services/hk-visas/visit-transit/visit-visa-ent...
Mainland residents making business trips to Hong Kong need to obtain an Exit-entry Permit for Traveling to and from Hong Kong and Macao, as well as an "endorsement for business visit (Shangwu)" from the relevant Public Security Bureau Office.
"Endorsement for business visit" is good for either single journey or multiple journeys to Hong Kong within its validity from 3 months up to 1 year and each stay of not more than 7 days in Hong Kong.
More information about Mainland Business Visit Endorsements: