From Chengdu. You can get here from Chengdu by taking a bus to Yibin and then taking a number 4 local bus across town to the Yibin South bus station Nan An. From there you can catch a bus to the park entrance. The last bus leaves from Yibin to the park at 4pm. It is also possible to hire a taxi from Yibin to the park for around ¥200.
From Chongqing. Bus from Chonqind to Yibin costs ¥90 and takes 4-5 hours.