The invention relates to the technical field of agricultural machinery, in particular to a device and a method for harvesting water chestnuts. The device comprises a travel machine and a framework. The travel machine is provided with a hydraulic suspension system, the hydraulic suspension system is connected with an engine of the travel machine and comprises a transmission case and a hydraulic cylinder, a rotary shaft I of the transmission case is in transmission connection with a rotary shaft II and is in transmission connection with a smashing mechanism, the smashing mechanism is mounted atthe rear of the travel machine, a shovel plate which is in running fit with a front bin is arranged at an inlet of the front bin, a push plate vibration mechanism is mounted in the front bin, a mud pump and a high-pressure air pump are mounted on the framework and are powered by a power generator of the engine, a water and air mixing cleaning mechanism is mounted in a transport bin, a water pipe is connected with a water outlet of the mud pump, a plurality of groups of spray nozzles are mounted on the water pipe, and an air delivery pipe is connected with an air outlet of the high-pressure airpump. The device and the method have the advantages that the water chestnuts can be thoroughly cleaned by five times, damage can be reduced to a great extent in harvesting procedures, the harvestingefficiency can be improved, and the harvesting cost of growers can be reduced.