Variations in seed water content during the day and harvesters inadequate adjustments during the harvest process can influence the physical and physiological performance of seeds. Thus, the aim of this study was to evaluate the performance of soybean seeds (Glycine max (L.) Merrill) throughout the harvesting process using tools of statistical process control. In the field of soybean seeds production, samples were collected from two harvesters in pre-established periods and submitted to seed  water content determination in the field and laboratory. Subsequently, purity, mechanical damage, germination, vigor (accelerated aging and electrical conductivity) and seedling emergence in the field were evaluated. Seed water content at the moment of the harvest associated with alterations in the rotational speed of the cylinder and in the opening of the cylinder/concave were sufficient to generate variability in the process, defined by random and special causes and also to promote reduction of soybean seeds performance. Changes in environmental conditions and seed water content of soybean seeds require proper adjustments of the harvester regulations, causing no damage to the seeds and making the harvesting process efficiently. The control charts allow to identify differences between the harvesters and its impact on performance of soybean seeds, to supervise the harvesting process and improve the effects in a continuous and permanent way.