A handheld window cleaning machine having a wastewater separation structure, comprising: a shell assembly in which a water-air separation unit is accommodated; a water tank assembly provided at a bottom of the shell assembly, a wastewater separation unit being provided in the water tank assembly, an outlet of the wastewater separation unit being in communication with an inlet of the water-air separation unit; and a suction nozzle assembly pluggably connected to a front end of the shell assembly, an outlet of the suction nozzle assembly being in communication with the wastewater separation unit; wherein an air outlet of the water-air separation unit is open outward, and a wastewater backflow opening is provided at a bottom of the water-air separation unit, and the wastewater backflow opening is in communication with an inlet of the wastewater separation unit; the water-air separation unit comprises a water-air separation body; the suction nozzle assembly comprises a suction nozzle upper cover, a suction nozzle and a suction nozzle lower cover, which are arranged sequentially from top to bottom to form a sandwich structure; characterized in that, a suction nozzle lock buckle is arranged in a center of an upper end of the suction nozzle upper cover, a first wastewater outlet is arranged on a bottom of an inner side of the suction nozzle lower cover; the suction nozzle comprises suction nozzle cover plates which are covered up and down together to form a converging cavity and a suction nozzle lower cover rubber coating, a front end of the suction nozzle lower cover rubber coating is led from the suction nozzle assembly, to form an led-out end, a suction nozzle strip is arranged on the led-out end, a wastewater suction opening of the suction nozzle assembly is formed between the led-out end and the suction nozzle strip, and a bottom of an inner side of the converging cavity is in communication with the first wastewater outlet; and a suction nozzle joint is fixedly provided at a front side of the water-air separation body, a lock buckle hole is arranged at a front end of the suction nozzle joint, the suction nozzle assembly is connected in the lock buckle hole through the suction nozzle lock buckle, and a second wastewater outlet is arranged on a bottom of an inner side of the suction nozzle joint, and the first wastewater outlet is butted with the second wastewater outlet. a shell assembly in which a water-air separation unit is accommodated; a water tank assembly provided at a bottom of the shell assembly, a wastewater separation unit being provided in the water tank assembly, an outlet of the wastewater separation unit being in communication with an inlet of the water-air separation unit; and a suction nozzle assembly pluggably connected to a front end of the shell assembly, an outlet of the suction nozzle assembly being in communication with the wastewater separation unit; wherein an air outlet of the water-air separation unit is open outward, and a wastewater backflow opening is provided at a bottom of the water-air separation unit, and the wastewater backflow opening is in communication with an inlet of the wastewater separation unit; the water-air separation unit comprises a water-air separation body; the suction nozzle assembly comprises a suction nozzle upper cover, a suction nozzle and a suction nozzle lower cover, which are arranged sequentially from top to bottom to form a sandwich structure; characterized in that, a suction nozzle lock buckle is arranged in a center of an upper end of the suction nozzle upper cover, a first wastewater outlet is arranged on a bottom of an inner side of the suction nozzle lower cover; the suction nozzle comprises suction nozzle cover plates which are covered up and down together to form a converging cavity and a suction nozzle lower cover rubber coating, a front end of the suction nozzle lower cover rubber coating is led from the suction nozzle assembly, to form an led-out end, a suction nozzle strip is arranged on the led-out end, a wastewater suction opening of the suction nozzle assembly is formed between the led-out end and the suction nozzle strip, and a bottom of an inner side of the converging cavity is in communication with the first wastewater outlet; and a suction nozzle joint is fixedly provided at a front side of the water-air separation body, a lock buckle hole is arranged at a front end of the suction nozzle joint, the suction nozzle assembly is connected in the lock buckle hole through the suction nozzle lock buckle, and a second wastewater outlet is arranged on a bottom of an inner side of the suction nozzle joint, and the first wastewater outlet is butted with the second wastewater outlet.