What does 常务 mean in an official title? I have already met this phrase on many occassions, I guess it means a ranking less than the No. 1 boss when it is used in an official title, like常务副校长 is less or lower than 校长.

But when I read a report made by a local government official at the 14th China-ASEAN Expo, I saw that he mentioned "中国国务院常务副总理张高丽“, but as far as I know, there is no such an official title like that for this man or this post in Chinese Cabinet. But perhaps he wants to make others notice this man is the important person, with a ranking higher than other vice premiers his colleagues.
This term "常务" is originally from a Japanese term "常務取締役". The Chinese and Korean are still using the direct translation. For Chinese, it's "常务董事". 

In an organization, the "常务" is more like "Executive". As the title suggests, they need to participate the daily operation of the organization rather than just providing dispassionate and objective criticism. 

Since "常务" seems closer to an organization from "someone within an organization"'s perspective. So usually "常务" rank higher than normal vice-title.