Abstract: High temperature is an important environmental factor affecting cotton yield. An experiment was conducted on the effects of short-term heat stress during the full bloom stage on fruit branch yield and yield components of island cotton; it is helpful to provide theoretical methods for breeding heat-resistant and stable-yielding varieties and formulating high-yield and stress-resistant cultivation techniques for island cotton. Using 'Xinhai 43' and 'Xinhai 49', a warming shed was set up in the field during the full bloom stage, and treatments of four warming levelslasting for 0 (control), 3 (H3), 6 (H6), and 9 d (H9) were employed to simulate the effects of short-term high temperature stress. The effects of temperature increase on dry matter accumulation, net photosynthetic rate, abscission rate of squares and bolls, yield, and yield components were analyzed. The results showed that short-term heat stress at the full bloom stage resulted in a significant increase in abscission rate of squares and bolls of the middle fruit branch of 'Xinhai 43' and 'Xinhai 49', and total dry matter accumulation of cotton plants decreased. At 30-50 days after anthesis, the dry matter of cotton bolls was significantly lower than that of the control. However, at 40-50 days after anthesis, the dry matter of the stems and leaves of two varieties with H6 and H9 treatments were significantly greater than those of the control. As the growth process progressed, compared with the control, the maximum dry matter of 'Xinhai 43' and 'Xinhai 49' with H3, H6 and H9 treatments decreased by 8.9%, 29.3% and 36.3%, and 11.8%, 28.1%, and 42.6%, respectively; and the daily average accumulation of cotton bolls decreased by 10.9%, 32.8%, and 42.2%, and 12.8%, 30.3%, and 45.9%, respectively. The time needed to reach the terminating date of fleet accumulation period increased by 5, 8, and 14 d, and 1, 5, and 10 d in 'Xinhai 43' and 'Xinhai 49', respectively. During the warming treatment, the P_n of the two varieties leaves decreased significantly with longer warming duration. After the end of warming, the senescence rate of P_n in each treatment was different. At the later stage of reproductive growth (40 days after anthesis), the P_n of leaves treated with H3, H6, and H9 was higher than those of the control, and in the order of H9 > H6 > H3 > CK. Short-term high temperature resulted in a significant decrease in boll number per plant, boll weight, and lint percentage. Among them, the coefficient of variation of boll number per plant (15.4% to 18.5%) was the largest, and the coefficient of variation of lint percentage (4.1% to 4.7%) was the smallest. Under the treatments of H3, H6, and H9, the boll number per plant of 'Xinhai 43' and 'Xinhai 49' decreased by 21.6%, 22.5%, and 28.9% and 16.6%, 26.4%, and 34.7%, respectively. However, the warming significantly increased the number of bolls in the upper fruit branches, and the number of bolls in the upper fruit branches of 'Xinhai 43' and 'Xinhai 49' increased by 0-24.9% and 2.7%-58.2% compared with the control. This, in turn, increased the yield and yield contribution rate of the upper fruit branches. Among varieties, the decrease in P_n, boll number, boll weight, and abscission rate of squares and bolls of 'Xinhai 49' were greater than those of 'Xinhai 43', suggesting that 'Xinhai 43' has better heat resistance.