Structure, cotton harvesting principal and main working parameters of rubber-bar roller harvester were studied in this paper. K value of rubber-bar roller speed ratio was determined based on displacement and velocity equations of rubber-bar end established by work pattern of the roller. The functional relationship between K value and harvest angle β of cotton plant by rubber-bar was derived. Additional, t Additional, the effects of K value on angle β and cotton harvesting performance were analyzed. The experimental results showed that collect rate of cotton was above 95% and percentage of impurities was less than 18% when working speed was 3 km•h-1 and K value ranged between 6.8～8.3.