Abstract: 【Objective】 To explore the optimal irrigation frequency for cotton under film drip irrigation in southern Xinjiang. 【Methods】 This experiment used Xin luzhong 54 as the experimental cotton. Through field experiments, four different irrigation frequency treatments were set up: 2 d/time (D₂), 4 d/time (D₄), 6 d/time (D₆), and 8 d/time (D₈). The conventional irrigation (CK) of farmers was used as a control treatment to study the response of cotton growth indicators, yield composition, and water use efficiency to different irrigation frequencies. Finally, the objective analysis entropy weight method was used to optimize the irrigation frequency suitable for subsurface drip irrigation in southern Xinjiang. 【Results】 Increasing irrigation frequency could promote the growth of cotton plant height, stem diameter, and biomass, and reach the maximum value during the opening period. D₂ treatment significantly increased by 9.53%, 20.83%, and 32.03% compared to CK treatment (P<0.05); with the increase of irrigation frequency, the number of bolls per plant and yield of cotton gradually increased. The D₂ treatment produced the highest number, reaching 9.21 and 7,546.35 kg/hm² respectively, but the water consumption was also the highest, at 477.80 mm. The D₄ treatment had the highest water use efficiency, at 1.59 kg/m³; The entropy weight results showed that D₂ treatment had the highest evaluation result. 【Conclusion】 The experimental results show that under the film drip irrigation of sandy loam soil in southern Xinjiang, when the irrigation quota during the growth period is 3,750 m³/hm², the entire growth period is irrigated 40 times, and the optimal irrigation cycle is 2 days.