Abstract: Abstract: When the sunflower combine harvester is operating in the field, the header reel may collide with the sunflower disk in the process of reeling, easily leading to the seeds dropping off the sunflower disk. The surface of the seed is subject to friction force, even damage to the seed hull, during the process of transporting seeds and sunflower disks with the spiral augers and elevator components. In addition, the severe vibration of the header can also cause the straw to shake, resulting the high seed loss. In this study, several experiments were carried out to explore the influence of the header collision and vibration on sunflower seed loss and the influence of the friction on the seed hull damage under different seed moisture content during the harvest period. The proper time of sunflower harvesting was determined to balance the contradiction between falling seeds loss and seed hull damage. The harvesting effect was also improved in the sunflower combine harvester. Firstly, a series of investigation was conducted to determine the impact of the collision of the reel web on the sunflower plate falling seeds loss during reeling, while the effect of the screw auger conveying on the hull damage of the sunflower seeds. The results show that the higher the moisture content of the seeds during harvesting, the greater the binding force between the seeds and the sunflower plate was, while the easier the damage of the seed hull was, and the greater the damage rate of the seed hull, was. There were less likely the seeds to fall off when they were hit. The optimal harvest time was considered to balance the comprehensive influence of the seed loss rate and the seed damage rate. Secondly, the weights of the sunflower plate falling seeds loss rate and the seed hull damage rate on the harvesting effect were 0.54 and 0.46, respectively, according to the requirements of sunflower harvesting on the loss rate and skin loss rate. The objective function was optimized with the Matlab platform. Thus, the moisture content of about 10.8% (9-13%) was the best harvest period for sunflowers. Finally, the Default Shaker hydraulic shaking,table was utilized to clarify the influence of vibration excitation in the main vibration frequency range of combine harvester on the falling seeds loss of the sunflower plate. The results show that the first-order vibration frequency was 7 Hz with a great impact on shattering, and the second-order vibration frequency was 19 HZ. The loss rate of sunflower plate shattering was 1.5% at most under the excitation of the first-order vibration. However, the theoretical vibration frequency of the reciprocating cutter was 7.08 Hz, similar to the first-order vibration frequency of the sunflower plant. The vibration excitation of the reciprocating cutter can cause the resonance of the sunflower plant during harvesting in the field, resulting in seed loss. The finding can also provide a strong reference to optimize the operation parameters of the key components of the header in the sunflower combine harvester.