2 typical soil in the Loess Plateau (Loess and Lou soil), 2 different rainfall intensities (45.5 mm/h and 95.5 mm/h) and 2 slope gradients (8.7% and 25.9%) were used to qualify the impact of 3 water quality (deionized, tap and saline water) on runoff and soil erosion in rainfall simulation. The results showed that the runoff rate acted differently between 2 types of soil. Tap water and saline water delayed the time of runoff yielding, but the runoff rate of deionized water grew more slowly than tap water and saline water under Loess. For Lou soil, deionized water always showed the highest runoff rate, while tap water and saline water were similar in ion amount, and did not differ in runoff rate. Water quality influence the runoff indirectly by the formation and development of crust. When precipitation was 45.5 mm, runoff amount significantly decreased with the increasing electrical conductivity, tap and saline rainwater decreased runoff depth by 5.7 mm and 1.7 mm for Loess, and by 7.2 mm and 9.8 mm for Lou soil, compared with deionized rainwater. The sediment yielding rate had significantly difference under different rainwater conditions and it was closely related to the runoff rate. Deionized water had a maximum sediment yield, while tap and saline rainwater decreased runoff depth by 45.9% and 35.8% for Loess, and by 65.6% and 68.3% for Lou. It should be noted that runoff and erosion was significantly affected by the quality of water in simulated rainfall. Deionized water was recommended for rainfall simulation to improve the accuracy and comparability of results.