This study determined the effects of mulching method on soil temperatures in the 0-20 cm soil layer, and grain yield of spring wheat (Triticum aestivum L.) in a semiarid rainfed agricultural area of northwestern China. The experiment was conducted at Tongwei Research Station, Gansu Agricultural University (34°55'N, 104°57'E) in 2012. The following 7 treatments were evaluated: plastic film mulch applied in summer (T₁), plastic film mulch applied in autumn (T₂), plastic film mulch applied in spring (T₃), mulching with chopped wheat straw (5 cm in length) on the soil surface in summer (T₄), mulching with whole wheat straw in summer (T₅), T₁ in combination with harvested wheat straw returned to the field (T₆), and control (no mulching, CK). Soil temperatures were measured and recorded at 32 points in each treatment. Soil temperatures differed significantly among mulching treatments, growth stages and soil layers. The largest difference in soil temperature occurred from the sowing to tillering period, followed by the dough stage to maturation period, whereas the smallest differences in soil temperature were in the jointing-middle filling stage. Soil temperature decreased with soil depth in the order 5 cm > 10 cm > 15 cm > 20 cm. Soil temperature in the T₆ plots was significantly (0.57 ℃) higher than, and this effect was more pronounced in the sowing, tillering, and maturing stages than in the other growth stages. The other five treatments either increased or decreased soil temperatures depending on growth stage and soil layer. Soil temperature was consistently increased by plastic film mulch but consistently decreased by straw mulching. The T₄ treatment had 9 points with soil temperatures higher than the CK, and 23 points lower than the CK. Mean soil temperature over the whole growth period was 0.63℃ lower in the T4 treatment than in the CK, with the difference being more obvious at the time of sowing and the tillering stage. Average soil temperatures over the whole growth period were in the order: plastic film mulch > CK > straw mulching. The highest difference occurred between T₆ and T₄ in the 5 cm soil layer at the tillering stage, with T₆ being 4.23 ℃ higher than T₄. The largest variation soil temperature among growth stages was found in the T₄ treatment, with a coefficient of variation of 32.4%. Mulching increased the number of kernels per spike by 17.4% to 36.3% compared with the CK. Mulching increased wheat grain yield by 21.7% to 37.3% compared to the CK, with the maximum yield increase being with plastic film mulch applied in the autumn (T₂). The exception was the T₅ treatment which decreased grain yield by 14.1% compared to the CK. It appears that the T₂ mulching method is the most suitable for spring wheat production in rainfed agricultural regions of northwestern China. There were highly positive correlations (r = 0.77^*-0.92^**) between soil temperature and plant height at jointing-flowering, but mulching method did not have a significant impact on spring wheat grain yield in the study area.