According to the harvest characteristics of low yield per unit and grass ratio of gramineous herbage seeds, high moisture content of plant stem and leaf when the seeds matured, and not suitable for all feed gain, the harvest principle of threshing prior to cutting was proposed. The main working parts, such as collector, brush roller and whole structure were designed. Also the parameters were selected. Test results listed as follows: the working speed of 9.0~9.7 km/h. When it was used to harvest elymus dahuricus, elymus sibiricus and Chinese wildrye, the harvest ability were 2.8 hm2/h, 2.8 hm2/h and 2.6 hm2/h, respectively. The comb brush loss rate were 1.41%~1.43%, 1.33%~1.51% and 1.54%~1.70% respectively. The fuel consumption of harvesting elymus dahuricus was 24.6~25.6 L/hm2. The imports of wind speed, leakage of wind speed and the exhaust wind speed of harvesting machine were 19.0 m/s, 14.9 m/s and 3.9 m/s, respectively.