we have to go Safflower hill, Shenzhen. how can we go from Changsha

Hi, but do you mean the Safflower Hill Park at Baoan District of Shenzhen? If so, you can take a trian from Changsha to Shenzhen first. It takes about 10-11 h for the whole journey.
Then you can take subway Luobao Line and get off at Airport East Station. Then walking to Yifeng Hotel Station, you can transfer to bus no. 301 to Shangniancunkou Station. After that, you can walk to the park.