Straw cover is commonly used in agriculture to reduce soil water loss and improve crop productivity. However, the effects of straw length and cover amount remain unclear. This study, conducted from 2020 to 2022 in double-cropping (Laixi County) and mono-cropping (Qingyuan County) systems, examined the impact of straw length, cover amount, and tillage methods on soil properties, crop growth, yield, and water use efficiency (WUE). Five treatments were tested: no till (NT) with long and full straw cover (LF), long and half straw cover (LH), short and full straw cover (SF), short and half straw cover (SH), and no straw cover (NS). The results showed that straw cover improved soil temperature, crop growth, yield, and WUE. Under the NS treatment, the 30-day average soil temperature was 0–1.22 °C lower than with straw cover. Meanwhile, WUE increased by 2.38% to 5.52% under straw cover treatments compared to NS. Consequently, the straw cover treatments resulted in an increase of 2.28% to 6.89% in crop yield compared with the NS treatment. In double-cropping systems, SH treatment had the best results, while LF treatment was most effective in mono-cropping systems. These findings suggest that straw cover can enhance water conservation and soil quality while improving crop yields.