This article studied the factors affecting the quality of cotton yarn. The properties of cotton fiber and their changes in technological processes play an important role in product production. Therefore, cotton fibers with different staple lengths of 28.5, 29.0, and 29.5 mm were used in the test work. Because it is advisable to use long fiber cotton fiber to get single yarn spun for sewing threads, for each option, different twists on the thread, i.e. the number of twists in 1 meter of thread were 850, 900, 950 b/m. The strength of individual threads ensures the quality of the product obtained from it, so we use the above number of twists. In order to determine the relative breaking strength of a single thread for sewing threads, experimental tests were conducted. According to the conducted experimental tests, 2 incoming factors were selected. As an output parameter, the relative tensile strength of the yarn, sN/tex (U) as input parameters, the effect of fiber staple length in mm, and the number of twists on the b/m indicator were studied based on the experiment. As a result of theoretical studies, the optimal value of the relative breaking strength of the thread from 16.25 sN/tex to 17.54 sN/tex, the staple length of the fiber should be more than 29.5 mm, and the number of twists should be 900 twist/meter It was determined that it should be. Based on the obtained conclusions, scientific and research work was carried out in the control enterprise. Based on the results of this research, the preliminary results of choosing the direction of further research were obtained. For this, LOTs were organized in the enterprise in various options. LOT-1 consists of Porloq-4, LOT-2 Bukhara-102, LOT-3 Sultan varieties. Based on the research results, the coefficient of variation in the linear density of yarns with different fiber content, the coefficient of variation in the number of twists, breaking strength, the variation coefficient in breaking strength, elongation at break, the coefficient of variation in elongation at break, comparison of the coefficients of variation for breaking strength and specific breaking strength were studied. When analyzing the effect of the composition of the fiber mixture on the physical-mechanical properties of the yarns for 3 LOTs, it was seen that the quality indicators of the yarns obtained from the LOT-1 mixture are higher than the indicators of the yarns obtained from other mixtures.