I would like to know if there is any transportation which connects Chengdu to Leshan?

The Intercity High-Speed trains connect Chengdu to Leshan. As Mt. Qingcheng is in another direction, you have to get back to Chengdu and change bus to Mt. Qingcheng. Then take bus to Dujiangyan, where you can find a bus to Huanglong and Jiuzhaigou, which takes around 6-7 hours. You have to stay overnight in Dujiangyan, as the bus departs at early morning. Or you can get back to Chengdu from Mt. Qingcheng and take bus to Huanglong directly.