The invention belongs to the technical field of waste heat recycling and power generation, and relates to an evaporator suitable for a steam waste heat type ORC power generation system. The evaporator comprises a cylindrical shell; a first tube plate is arranged on one end surface of the shell in the radial direction; a first shell cover is arranged on the outer side of the first tube plate; a first channel is formed between the first tube plate and the first shell cover; a steam inlet is formed in the position, close to the top of the first channel, of the first shell cover; a second tube plate is arranged on the other end surface of the shell in the radial direction; a second shell cover is arranged on the outer side of the second tube plate; a second channel is formed between the second tube plate and the second shell cover; a condensed water outlet is formed in the position, close to the bottom of the second channel, of the second shell cover; and a plurality of heat exchange tubes in the axial direction are arranged in the shell. The evaporator has the advantages that a plurality of tube passes are formed after tube bundles are layered, the specific volume of steam in the condensation process is decreased, the tube bundles where the condensed water flows are divided into the multiple tube passes equivalently, and therefore the flow rate of the condensed water can be increased, the heat transfer coefficient of the condensed water side can be enhanced, and the heat transfer efficiency can be improved.