Yes. During the peak season (from April. 1st to Nov. 15th), you have to pay the entrance ticket and sightseeing bus fee once again if you want to double enter Jiuzhaigou in 2 days, which is 310 Yuan in total.
While in the off season (from Nov. 16th to Mar. 31th), you only need to add 20 Yuan plus the sightseeing bus fee, which is 80 Yuan, to get the access for the double entry in Jiuzhaigou.