how can I travel by train from hong kong to nanchang?

At Hung Hom Railway Station, Hong Kong, take East Rail Line to Lok Ma Chau in around 40min. Then cross the border and walk to the Futian Checkpoint. There you can transfer to Shenzhen Longhua subway line to the North Railway Station. Three high speed trains are scheduled to Nanchang per day, leaving at 13:00, 16:32 and 18:32.

Hey, besides Shenzhen, you can also transfer in Guangzhou. Also in the Hung Hom Station, you can take a through train to Guangzhou East Rail Station within 2h. After that, take suwbay line 1 to Gongyuanqian and transfer to line 2 to the South Rail Station. 11 high speed trains leave for Nanchang and it takes only 4.5h.