My roomate told me that it had emerged when I woke up in the morning.
I didn’t go to bed until 1:30 for my homework. I was so tired that I fell asleep soon then missed the process.
This is Aeschnophlebia longistigma Selys, 1883
There are two special spots on its eyes
Unfortunately, it missed one leg during the eclosion
There is another nymph of this species in the water. I will try to capture the whole process of it next time.