China borders Nepal on the north side (with the Himalayas). Hence travelling from China to Nepal is possible by flight from various Chinese cities to Kathmandu, Tribhuvan airport or overland travel from Tibet to Kathmandu via China-Nepal (Kyirong) border. It would take approx 3 to 6 hrs time to fly from Kathmandu to Lhasa or Beijing and cost USD approx 600 for round trip flight. In the mean time Lhasa to Kathmandu overland trip is 7 days program and cost you approx USD 1000 per person.
China to Nepal