Train is the main way, hehe.
From Zhengzhou to Haikou, there is only T20 1/T204 without changing trains, but it seems a little difficult for you to buy a hard seat ticket (in fact, this train is very difficult because the starting station is Beijing West), or you can buy a ticket to transfer to Guangzhou or Zhanjiang. If you are not familiar with the traffic, it is not recommended to change to other trains, nor to change to boats or buses (trains are the most comfortable after all).
Haikou Railway Station to Haidian Campus
After leaving the station, you can find a taxi. Together with other people, you will always go to the school at ***60 in the evening, usually from the south gate or the west gate. You can rest assured that you can walk northeast.
There are buses to the bell tower during the day. After you leave the station, coordinate bus No.37 at the railway station, get off the bell tower, go to a bridge near it, and go straight ahead to see the west gate of Hainan University (you can also transfer to other buses to Haidian Island to Hainan University Station). Ticket price, 4 yuan.