The utility model discloses an evaporator, which can be particularly used in a cold water unit and solves a problem that the existing flooded evaporator is large in amount of refrigerant filling quantity and excessive in side resistance of a refrigerant, and the existing dry evaporator is lower in heat exchanging coefficient. The evaporator adopts a layering structure, and a heat exchanging tube is led to be totally immersed in refrigerating fluid in each layer of pallet, so that the evaporator has the advantages of the flooded evaporator of being high in heat exchanging efficiency. Simultaneously, the evaporator has a layering effect, space without the heat exchanging tube needs not store too much refrigerating fluid, so that the refrigerant filling quantity is greatly reduced, the side pressure of the refrigerant is greatly reduced when a machine is shut down, compact degree is higher, so that requirements of the cold water unit requiring low temperature difference and high power are satisfied.