Article: 

141(A)(1) says if the president is satisfied that a grave or economic life of Bangladesh or any part thereof, is threatened by war or external aggression, or internal disturbance he may issue a proclamation of emergency for one hundred twenty days.

So the main three reasons for issuing a proclamation of emergency are: 

i) Economic Emergency / Emergency life

ii) Emergency of war or external aggression and 

iii) Internaldesturbance

And if the reasons are satisfaction only the president can issue it for 120 days highest. And he has to make the decision with the consent of the prime minister.

How to revoke:

(2) (a) may be  revoked by a subsequent proclamation

(b) Shall be laid before parliament

(c) Shall cause to operate at the expiration of one hundred and twenty days.