Abstract: The field experiment was conducted to study the effects of different levels potassium fertilizer reduction application by stages on yield and quality of lettuce in purple garden soils. The results showed that the potash fertilizer reduction of 10% - 30% application by stages did not influenced lettuce yields at two experiment sites, the K2 treatment (reduction of K 10% amount of topdressing) had best effects included in the maximum yield (the increase of 4.2% and 4.5%) and the optimum economic profit (84923 yuan/hm₂ and 72075 yuan/hm₂). Vitamin C content of lettuce leaves showed a downward trend in potassium fertilizer reduction application by stages at two experiment sites, compared with the conventional fertilization (CK) the K2 treatment were significantly decreased vitamin C content of lettuce leaf (8.0% and 8.7%), but the changes of vitamin C content in lettuce stem was different. Potassium fertilizer reduction application by stages reduced nitrate content of lettuce leaves and stems at two experiment sites, the role of K4 treatment (minus the amount of potassium 30% equivalent to topdressing) was the maximum. Considering the balance of sugars in lettuce leaves and stems, K3 treatment was best. Essential amino acid content of lettuce leaves were increased significantly in potassium fertilizer reduction application by stages at two experiment sites but essential amino acid contents of lettuce stem were decreased. Amino acids quality traits of lettuce is the best in K4 and the second was K2. Comprehensive consideration of yield and quality of lettuce, the K2 treatment (reduction 10% potassium fertilizer application by stages) was the best in two purple vegetable soil.