Please read this
http://www.info.gov.hk/info/holiday_e.htm

And here has Hong Kong events calendar which provided by Hong Kong Tourism Board.
http://www.hkta.org/eng/showtime/calendar/index.jsp

FYI, this year is 10th Anniversary of the Establishment of the HKSAR. 1 July will have special events.
for more read, http://www.gov.hk/10