You should have a clear travel plan when buying railway tickets, as stated in the Railway Passengers Notice. A return fee amounting to 20 percent of the ticket fare is charged when the railway ticket is returned.

In case of a ticket to Kowloon in Hong Kong, 50 percent of the fare will be refunded if you return the ticket two days before the departure, and 70 percent if you return it three to 14 days before the departure.  You'll get 100 percent of the fare refunded if you return the ticket 15 days before the departure.  In all cases a HK$15 (17 yuan) commission fee will apply.