Finally I have got the bug from a very kind people, i don't know if he is here. Yes, he is! @Pipecraft
It has got to put a blank in a footnote, but unfortunately, there usually is no blank in a Chinese sentense. for example, the first footnote works fine, but the sencond one goes wrong without a blank:
正常的[1]
[1]: 正常的的注脚,必须至少包含一个 空格
有问题的2
正常的[^1]
[^1]: 正常的的注脚,必须至少包含一个 空格
有问题的[^2]
[^2]: 有问题的注脚,因为没有空格