The last years of the 20th century seams real changes in sportswear due to the rapid development in fabric structure, which provide the players with the compatibility between body movement and structure of clothes during doing the sport , with over looking to the composition of swimwear it needs special technique in order to get best performance which represented in ( seam strength – seam elongation – seam slippage – seam puckering – seam penetration force ) where many problems appears in production process in swimming wear has negative impact on the quality of products .The research aim studying the most effective sewing parameters which effect the functional performance of swimming wear which represented in needle number(65-70-75) , seam density (4-5-6 in centimeters) , seam types(301-304-504) by using research tools represented in questionnaire form to determine the defects of girls swimwear production , questionnaire form to evaluating the girls swimwear products after using the research result , swimwear analysis form, sewing machines , laboratory devices laboratory experiments to measure seam strength , seam puckering , needle penetration force , after preparing the samples which consist of research limitation knitted fabric 120 gsm with fabric content (95% cotton -5% lycra), and group of experts specialized in the manufacture ready – made garments the research result were extracted after doing Statistical treatment as-N- way ANOUVA , LSD, Radar chart , cooper, Alpha cronbach where the result of the research reached that the best seam type used in sewing knitted fabric for sewing wear and has high effect on seam strength and seam puckering is seam (504) and the best seam density which effect seam strength is (6 seam in centimeter) , the best needle number which effect needle penetration force is needle number 65