The invention discloses a technology for welding a carbon steel overlaying welding layer of a tube plate of a high pressure heat exchanger with a low carbon steel tube in a sealing way, comprising the following technological processes, i.e. a step one of welding carbon steel on the tube plate of the high pressure heat exchanger in a submerged arc overlaying way, thermally treating the overlaying welding layer and the tube plate under the condition of passing 100% UT (Ultrasonic Test) and 100% MT (Magnetic Test) flow detection, and increasing the overlaying welding layer to the range of 6mm to 8mm in a machining way, wherein the groove structure of the tube plate is in the form of an aligned groove, the low carbon steel tube is aligned with the overlaying welding layer of the tube plate, and the sealing welding groove of the overlaying welding layer of the tube plate is chamfered at 2*45 degrees; a step two of preheating to 80 DEG to 100 DEG before welding, and welding the low carbon steel tube in the groove of the overlaying welding layer of the tube plate in a point way before welding as well, wherein the point welding enables the root part to be thoroughly welded without welding sticks; a step three of implementing sealing welding on the groove by adopting an automatic argon arc welding, implementing 100% PT (Penetration Test) flow detection on the welded junction after the completion of sealing welding, and eliminating surface defects of the welding line. According to the technology for welding the carbon steel overlaying welding layer of the tube plate of the high pressure heat exchanger with the low carbon steel tube in the sealing way, the surface of the welding line of the carbon steel subjected to the sealing welding is smooth and flat, and no needle-like air holes are formed in the near surface and the surface of the welding line; therefore, the long-term scour by supplied water can be completely withstood.