Abstract: This study determined the effects of mulching time on soil temperature in 0-20 cm soil layers and soil moisture storage in 0-120 cm soil layers, and on potato yield (Solanum tuberosum) in a rain-fed agricultural area of Southern Ningxia. The experiment was conducted at Touying County, Guyuan City (106°44' E, 36°10' N) from 2013 to 2015. The following 4 treatments were evaluated: no mulching, plastic film mulch applied before sowing, plastic film mulch applied in spring, and plastic film mulch applied in autumn. Results showed that, compared with no mulching, all the treatments increased soil temperature, especially the autumn treatment, which was 1.0 ℃ higher than no mulching. They can also increase soil temperature during early spring and decrease temperature differences at the initial stage of potato growth. All the mulching treatments increased soil moisture storage at the initial stage and promoted water consumption during the tuber expanding stage, especially the autumn treatment. This promoting effect was evident mainly in the 20-60 cm soil layers, especially in dry years and years with average rainfall. Mulching with plastic film in autumn significantly increased potato tuber yields to 34543 kg/ha, 40.8% higher than the no mulching treatment, and there was a 23.5% increment in potato water use efficiency to 77.5 kg/(ha·mm). There were highly positive correlations between tuber yield, soil temperature and soil moisture storage during early spring, but significantly negative correlations with soil temperature before the sowing stage. In conclusion, the autumn plastic film mulching treatment can increase soil temperature and moisture during the early spring period and accumulate soil water depleted after the potato tuber expansion period. Results showed that this is an appropriate treatment which has a significant impact on potato yield.