hi. I interest solar power system in Shenzhen.

By train: take a train from Ulan Bator to Beijing first in around 28h. Go to Beijing West Station and take a bullet train to your destination directly and it takes around 9h. Train to Beijing costs CNY 1,222 for a hard sleeper and CNY 1,723 for a soft sleeper. The bullet train to your destination costs CNY1479.5 for a first class seat and CNY936.5 for a second class seat.

By air, Beijing also shall be a good transfer place. The total duration shall be around 25h. The air ticket fee changes from time to time. It is hard to tell you the cost without knowing your travel date. Anyway, you can try to search it out on the flight page of this website.