Drought is a widespread problem in crop growing areas and a threat to food security worldwide. Mulching has become an important practice for maintaining soil moisture, reducing weed growth, mitigating soil erosion and improving soil temperatures in arid and semiarid areas. In northeast China, winter snow is heavy and spring drought frequently occurs, partially due to the loss of melted snow water by evaporation in spring. As such, this study assessed the use of plastic mulching in potato crops to minimize drought by accumulating and reserving water from winter snowfall. In field experiments conducted at two locations in the Heilongjiang Province, China (Keshan in 2011 and 2013, Heihe in 2011 and 2012), black and colorless transparent films were used as mulch during the thickest snow from late winter to early spring. The effects of plastic mulching on soil moisture content and temperature at various soil depths and its influence on potato growth and yield were evaluated. The results showed that film mulching increased the temperature and moisture content of the plow layer (0–10 cm). Black film retained more solid snow than colorless film. The black and colorless films advanced potato emergence by 7 and 14 days, respectively, compared with the control; higher temperatures under the colorless film resulted in earlier emergence than under the black film. The colorless and black film mulching increased soil water contents by 2.5 and 1.5 percentage points, respectively, compared with the control. Average tuber yield over the three-year study at both sites increased by 68.6% and 110.9% with black and colorless film, respectively, with yield increases more apparent in the year with spring drought. The effect of film mulching on yield mainly depended on differences in soil water content between mulching treatments and the control. Snow conserved by winter film mulching supplied water to the plow layer. Our results revealed that film mulching in winter significantly increases soil moisture content, ensures good stand establishment, and effectively solves a severe problem with spring drought in northeast China.