Hi, can you let me know what's the temperature in Chengdu & Jiuzhaigou around 4/8 - 11/8?

Well, during that time, the average temperature of Chengdu could be about 28 C or a little higher and that of Jiuzhaigou could be about 18-20 C. And the temperature of Jiuzhaigou in daytime and at night varies much. Therefore, you might need shirt in daytime, but thin coat at night. Furthermore, the weather of Jiuzhaigou is changeable. It may suddenly rain but not frequent and heavy. Anyway, the weather forecast could help a lot then.