Are 17th July to 26th July 2015 school holidays in china?

Yes, according to local education bureau Chengdu, summer vacation begins on July 1 for primary schools and July 9 for middle schools. You know, some Chinese students may travel during the summer vacation. However, the attraction sites won't be crowded compared with national day holidays. I think you still can manage a trip to Chengdu and Jiuzhaigou Valley.