Shaghai Pudong airport to Sanmen

All the public transportation to your destination would be out of service upon your arrival and it would be quite costly to take a taxi or rent a car to get there. Therefore, I suggest you stay for a night in the city. In the next morning, take a bullet train at Hongqiao Railway Station to Sanmen County directly.
P.S. If possible, you'd better book the train ticket in advance in case.

Ok.If i book my bullet train ticket.How from i get it and where will i pay.

TravelChinaGuide, the website you are visiting, is able to help you book the train ticket. Book through them and they will deliver your ticket to your hotel (if you will stay in any hotel). Or you can directly collect your ticket in the train station with your passport then. If needed, here is their contact for your convenience:
bookingtravelchinaguide.com