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A variety of harvesting machines were developed to finish different harvesting works,，such as combine-harvester for wheat and rice, harvesting boat for aquatic plants in rivers and lakes, trailer mower for grassland. But these machines are not suitable for aquatic plants growing in orderly arranged pools in large-scale greenhouses, which are used to purify tail water from sewage plants, because water in these pools is deep and space inside greenhouses is not enough for these machines to work in. Additionally, combustion engines are usually used to supply power for existing harvesters, consequently noises and exhaust pollution are serious problems in closed greenhouses. Aquatic plants grow rapidly and need to be cut regularly, which need a lot of labor. To satisfy the need of plants harvesting in greenhouses, research work on the functions, the basic structure, as well as the design of electric control system of a new type of harvester were done. A group of batteries was used in the new harvester to supply power for motors, which were used to drive cutting device, walking system and rotating mechanism separately. When it was working, the harvester walked along two parallel tracks above pools in greenhouses, cut grass in pools and transferred the grass from the left to the right, and then laid down grass on passages between two adjacent rows of pools. By experiments and calculation, the key parameters for the above mentioned mechanisms, such as main sizes, cutting power consumption, motor power, and walking speed were decided. Harvesting tests showed that when the machine walked at 0.75~0.92m/s and average cutting speed of the cutter was 0.92m/s, good results can be achieved, there were no repeated-cutting or uncut areas. Harvesting efficiency reached 7500~9000m2/h, which was more than 20 times of artificial work.