This study examined the effect of replacing low-quality alfalfa hay (AH) with corn silage (CS) in basal forage diets on nitrogen (N) utilization and milk performance of crossbred Hu ewes at different lactation stages (LS1, 32-41; LS2, 84-93 days in milk). Diets used were CON (0% CS, 33.7% AH, 37.2% oat hay [OH]), CS1 (9.2% CS, 23.8% AH, 37.6% OH), and CS2 (18.5% CS, 13.8% AH, 38.0% OH). In a completely randomized design, 12 ewes received the diets formulated to have comparable metabolizable energy and protein content. The N intake was highest in CS2, and rumen degradable organic matter intake increased as the proportion of CS increased. The apparent nutrient digestibility was higher in CS diets than in the CON diet. The CS diets showed significantly lower urinary N excretion rate with their higher N retention rate compared with CON, indicating improved N utilization efficiency in CS diets. Compared with CON, CS2 increased milk yield by 36%, and CS diets increased milk protein and fat content. Overall, partial substituting CS for AH improved N utilization variables and lactation performance, suggesting that a CS-containing forage diet may enhance economic benefits of lactating sheep in the northwestern dryland regions of China.