Abstract: Three species of Gramineae grass, three species of Legume grass and three species of Asteraceae grass were collected from Ordos of Inner Mongolia in June, July and September respectively and air-dried. And twenty-seven samples were made. The comprehensive evaluation results by relative feed value （RFV） showed that Zhongmu No.2 had the highest quality when the same species of grass samples harvested in June, July and September were mixed. And the quality of Astragalus adsurgens Pall. and Artemisia desterorum Spreng were the next, and the quality of Hedysarum scoparium Fisch. was the worst. Then the same species of forage grass harvested at different time were compared. As for Gramineae grass, the nutritional value order of Stipa krylovii Roshev., Agropyron desertorum and Zhongmu No.2 in different harvesting period was June>July>September. As for Legume grass, the nutritional value order of H. scoparium and A. adsurgens in different harvesting period was June>July>September, but the nutritional value order of Melilotus albus was June>September>July. As for Asteraceae grass, the nutritional value order of A. desterorum, Artemisia scoparia Waldst. et Kit. and Artemisia sieversiana was July>June>September.