In the plain area, the fragmentation of the cultivated land unit is an important factor affecting the mechanical harvesting efficiency of wheat. Taking Dingzhou City in Hebei Province as an example, the fragmentation characteristics of cultivated land unit and the quantitative evaluation of mechanical harvesting efficiency of wheat were analyzed, and then the scenario mechanical harvesting efficiency of cultivated land unit after land merger was analyzed. It was found that the cultivated land unit in plain area was small and scattered，the plot was long and narrow, the ratio of length to width range was relatively large, which was not suitable for large-scale agricultural development work. The mechanical harvesting efficiency of cultivated land area affected the total work efficiency and work efficiency was increased with the increase of areas of arable land and land consolidation, the total operating efficiency can reach 0.4301s/m2 in theory, and the efficiency can reach 0.3049s/m2. When the cultivation unit of land area reached 8500m2, the mechanical harvesting efficiency of wheat would get into full play. The total operation time and pure working time would be reduced by 38.64% and 43.11% after parcel union, respectively. The plain area should be carried out cultivation unit of land ownership adjustment and land circulation on a large scale, the contiguous area of cultivated land reached a certain scale, which can effectively improve the mechanical harvesting efficiency of wheat, and reduce the unloading time and other time. The research can provide theoretical support for land consolidation in plain area.