The objective of this study was to ascertain the best irrigation methods through researching the effects of different irrigation on alfalfa biological characteristics and biomass by a randomized block experiment. The main conclusions were as follows:(1)The leaf area of alfalfa increased from branching period to full flowering period，Irrigation quantity increased shoot/leaf ratio unremarkably; The bigger height of alfalfa appeared at higher irrigation quantity. (2) Budding period is the key stage affecting fresh biomass formation, so reasonable irrigation should be carried out at this time to improve the leaf area，height and output.