Effects of using different year of humic acid on millet growth and water and fertilizer use efficiency was studied in a field experiment in a semi-arid and arid region in 2011-2014. Four-year results showed that after using humic acid, the soil moisture content was increased by 0.20%-40.41% over that of CK, and it mainly affected soil moisture content of 0-40cm soil layer, the differences decreased with soil layer depth increasing; plant height and dry matter weight were increased by

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... % and 0.59%-236.81% respectively over that of CK; grain and biological yield were significantly increased by 1.09%-14.76% and 0-25.27% over that of CK, and the effect of current year with the continuous use ofuse of humic acid is best, and the fourth-year effect of treatment only with the use ofuse of one-year humic acid had no significant differences compared with CK; water and fertilizer was similar to the variation of yield. In a word, the use of humic acid could improve the condition of soil water and fertilizer, make full use of limit water resource, increase yield, thus it could increase water and fertilizer use efficiency, and reduce environmental pollution, treatment by continuously using 4year humic acid was best.