Here is one method:

Aftee going through the Luohu Border, please take the KCR East Rail to Kowloon Tong and then transfer to Kwun Tong Line to Diamond Hill station. Finally, at the bus terminal of Exit A1 here, you could take bus No.91 to HKUST directly. The train fare is HKD38 and the bus fare is HKD6.4.

Thanks Sisley, That sounds good.