駐內地工作的香港人應如何報稅?須要同時交香港及內地稅嗎?

Yes if some conditions are met. However, the same amount will not be double taxed. Please see the PDF file.
This booklet discusses tax issues that may concern a Hong Kong resident exercising employment both in Hong Kong and in the Mainland of China.

http://www.ird.gov.hk/eng/pdf/pam63e.pdf
Brief explanation of how "The Arrangement between the Mainland of China and the Hong Kong Special Administrative Region for the Avoidance of Double Taxation on Income" applies to an individual
http://www.ird.gov.hk/eng/pdf/dt_ps_e.pdf
FAQ : Double Taxation Relief
http://www.ird.gov.hk/eng/faq/dta_2006.htm