I am planning to visit Kashgar from Chengdu.

Well, neither direct train nor long-distance bus operate between these two places.

By train, you can take a transfer at Urumqi South Railway Station first. It takes around 1 day and 23 hours on the way. Then transfer the train to your destination. The duration is about 23 hours.

Or you can take the direct flight from Chengdu. It takes 6 to 7 hours on the way. This shall be the best way to go!