Water-saving rice systems must maintain yield targets while reducing water consumption. Applying biodegradable film to cover the soil surface reduces water loss through evapotranspiration, establishing a warmer, more humid microenvironment for rice growth compared to traditional paddy rice systems.  This study examined soil water regimes for rice production in Northeast China, comparing rice growth with and without biodegradable mulch film under continuous flooding, drip irrigation, and controlled irrigation conditions.  The implementation of biodegradable mulch film elevated soil temperature and sustained soil moisture during early rice development.  Continuous flooding with biodegradable mulch film yielded the highest rice production (9.4 Mg ha^–1) and net profit of approximately 11,800 CNY ha^–1.  Drip irrigation with biodegradable mulch film achieved maximum water efficiency, demonstrating the highest water productivity (1.25 kg m^–3) and minimum water consumption (235 mm).  Root length, weight, and surface area in the 0–40 cm soil layer exhibited positive correlations with water productivity, shoot dry matter, and yield, indicating that root morphological characteristics, particularly during the panicle initiation stage, enhanced rice production and water conservation.  The findings demonstrate that biodegradable mulch film created favorable soil conditions for root proliferation, enabling higher yields in water-saving rice systems.