Abstract: Abstract: Mulching is of functions of warming, preserving soil moisture, suppressing salt and preventing weeds, increasing soil water storage capacity, reducing soil water evaporation and improving the effectiveness of soil moisture. A cotton cultivation field experiment was carried out under drip irrigation with plastic film mulching for 2 growing seasons from May to September of 2016 and 2017 in the Tarim Basin, Northwest China (40°06 N，80°44 E, altitude 1 025 m). The experiment included 6 mulching duration treatments of 40 (J1), 55 (J2), 70 (J3), 85 (J4), 100 (J5) and 140 d (whole growing season mulching, CK). The air temperature and precipitation were measured. The precipitation during the growth period of cotton was 45.2 mm in 2016 and 132.36 mm in 2017. The cotton sowed on April 8th, 2016 and April 15th, 2017. The seedling stage started from April 30th in 2016 and May 10th in 2017. The duration from seedling to boll-opening stages was 137 and 131 days respectively for the year of 2016 and 2017. The soil temperature was measured at 10 cm depth. The water content was determined for 0-80 cm soil depth. Effects of plastic mulching duration on soil temperature, soil water content, crop evapotranspiration (ETc) and yield of cotton field. The water use efficiency was also calculated. The results showed that soil temperature was greatly affected by film mulching duration. After the film was removed, the soil temperature was decreased especially at seedling and bud stage. For the whole growing period of cotton, the change in soil temperature of CK was similar with J5. The film mulching duration also affected soil water content. The soil water content was lower during the early stage of cotton than after the flowering stage. The water content was the lowest for J1 and J2 treatments at the seedling and bud stages since the film was removed and evaporation was higher than the other treatments during these stages. The change of soil water content at 0-20 cm was obvious for different mulching duration treatments. The average soil water content was significantly lower by 14.5%, 10.7%, 8.7% and 7.5% for J1, J2, J3 and J4, respectively than CK (P<0.05). The average soil water content of J5 was not significantly different from that of CK (P>0.05). The ETc of CK and J5 was not different significantly (P>0.05), and that of CK was significantly lower than that of J1-J4 (P<0.05). Among all the treatments, the cotton seed yield of J5 was the highest (P<0.05) with the 2-year average of 6 800 kg/hm2 and the WUE was also the highest with the 2-year average of 11.5 kg/(hm2· mm) (P<0.05). The yield and WUE of J5 was not significantly different from CK (P>0.05). According to the relationship between film mulching duration and soil water content, ETc, WUE and cotton seed yield, the soil water content, yield and WUE increased but the ETc decreased with the duration. However, when the duration was higher than 100 d, the water content, yield and WUE decreased but the ETc increased. Thus, mulching duration of 100 days was suggested as an optimal treatment since the yield and WUE was the highest and the ETc was lower. The results could guide the film application in southern Xinjiang and provide valuable information for degradable film manufacture and recovery.