Abstract: A parallel flow evaporator comprises a transitional plate. A left side plate and a right side plate are connected with two side edges of the transitional plate respectively. A first liquid inlet manifold is secured to an upper side edge of a forward side surface of said transitional plate, a first gas outlet manifold is secured to an upper side edge of a rearward side surface of said transitional plate, a second liquid inlet manifold is secured to a lower side edge of the forward side surface of said transitional plate, and a second gas outlet manifold is secured to a lower side edge of the rearward side surface of said transitional plate. A plurality of flat tubes, which are parallel with and distant from each other, are arranged between said first liquid inlet manifold and said second liquid inlet manifold. Said first liquid inlet manifold and said second liquid inlet manifold as well as said first gas outlet manifold and said second liquid inlet manifold communicate with said flat tubes.