Well there is flight from Hangzhou and Lhasa with a stop in Mianyang city, Sichuan province, or at Dazhou, Chongqing. From Hangzhou to Lhasa, however, there is no direct train yet. You can consider to take the train via Xi’ning. From Hangzhou you can easily get to Shanghai or Xi’an or Xi’ning and then from here, you can fly or take the train to Lhasa. For more details, please read further on how to travel to Lhasa, Tibet.