In order to provide references for confirming requirement of calcium (Ca) and phosphorus (P) for Yili mares during lactation period, the effects of dietary Ca and P levels on body weight, heart girth, nutrient apparent digestibility and metabolism and plasma physiological-biochemical indices were examined. Twenty-five Yili mares in their end of the 2nd lactation month with similar age (11 to 14 years old), body weight [(371±21) kg] and parity (4 to 6 parities) were selected, and allocated to five groups of 5 animals each. In the 3rd lactation month, the Ca feed level of mares in groups Ⅰ, Ⅱ, Ⅲ, Ⅳ and Ⅴ was 45.03, 48.50, 51.96, 55.43 and 58.89 g/d, and the P feed level was 30.05, 32.03, 34.01, 35.99 and 37.97 g/d, respectively. In the 4th and 5th lactation month, the Ca feed level of mares in groups Ⅰ, Ⅱ, Ⅲ, Ⅳ and Ⅴ was 43.60, 46.42, 49.25, 52.07 and 54.92 g/d, and the P feed level was 27.63, 29.24, 30.86, 32.47 and 34.12 g/d, respectively. The trial lasted for 90 days, and every 30 days for a test cycle. The results showed as follows: dietary Ca and P levels had no significant effects on body weight, heart girth and the apparent digestibility of dry matter (DM), organic matter (OM) and neutral detergent fiber (NDF) (P>0.05). The apparent digestibility of crude protein (CP) of group Ⅴ was the highest, and increased by 12.26%, 12.37% and 18.28% (P<0.05) as compared with group Ⅱ, Ⅲ and Ⅳ, respectively. The apparent digestibility of gross energy (GE) of group Ⅰ was the highest, and increased by 8.32%, 7.19% and 11.24% (P<0.05) as compared with group Ⅱ, Ⅲ and Ⅳ, respectively. The apparent digestibility of Ca of groups Ⅰ and Ⅲ was higher than that of group Ⅳ, and increased by 17.74% and 14.49% (P<0.05), respectively. The apparent digestibility of P of group Ⅲ was the highest, and increased by 35.39% (P<0.05) as compared with group Ⅱ. Dietary Ca and P levels had no significant effects on nitrogen and Ca metabolism (P>0.05). The metabolic energy (ME) of group Ⅰ was higher than that of groups Ⅱ and Ⅳ, and increased by 7.95% and 11.33% (P<0.05), respectively. The energy retention rate of group Ⅰ was higher than that of groups Ⅱ, Ⅲ and Ⅳ, and increased by 9.30%, 8.50% and 12.10% (P<0.05), respectively. The P retention of groups Ⅰ, Ⅲ, Ⅴ was significantly higher than that of group Ⅱ (P<0.05), and group Ⅲ was the highest among groups which increased by 42.59% (P<0.05) as compared with group Ⅱ. The P retention rate of groups Ⅰ and Ⅲ was significantly higher than that of groups Ⅱ and Ⅳ, and group Ⅰ was the highest among groups which increased by 49.67% and 46.32% (P<0.05) as compared with groups Ⅱ and Ⅳ, respectively. The P utilization rate of groups Ⅰ, Ⅲ and Ⅴ was significantly higher than that of group Ⅱ (P<0.05), and increased by 17.74%, 18.80% and 16.79% as compared with group Ⅱ, respectively. The levels of plasma ionized calcium (Ca²⁺), P, calcitonin, bone gla protein, placental prolactin, pituitary prolactin, estradiol, progesterone and estrone showed no significant difference (P>0.05) when mares fed with different levels of dietary Ca and P. Moreover, the level of plasma parathyroid hormone of group Ⅲ was significantly higher than that of groups Ⅳ and Ⅴ with an increase of 70.61% and 47.58% (P<0.05). In conclusion, diet Ⅰ (the Ca and P feed levels in the 3rd lactation month are 45.03 and 30.05 g/d and those in the 4th and 5th lactation month are 43.60 and 27.63 g/d, respectively) can meet the Ca and P requirements of Yili mares during lactation period. Suitable dietary Ca and P levels are beneficial to maintain higher apparent digestibility of gross energy and Ca, retention and utilization of P and energy.