Abstract: In order to provide theoretical basis for rational fertilization in loess plateau, a field experiment was conducted to test the effect of different bio-organic manures on grain yield and water use efficiency of oil flax.The experiment included following treatments:HA organic fertilizer (T1), Yisa 803 bio-organic manure (T2), Lvnengruiqi refined organic fertilizer(T3), Jinfufeng soil conditioner (T4), Heizhenzhu bio-organic manure (T5) and Baaiwo bio-organic fertilizer(T6); Non-fertilizer as a control(CK).The results showed that the dry matter accumulations per day with bio-organic manures reached a peak value between full flowering and young fruit stages and increased by 3.92%~11.6% over that with CK.At maturity stage, CK was with the most ratio of dry matter in stem, spike axis and kernel husk, and T6 was with the most ratio of dry matter in leaf; while T4 was with the most ratio of dry matter in grain and T2 was the next, increasing by 31.0% and 26.2% compared with CK, respectively.Compared with CK, all treatments increased the biological yield of oil flax by 2.03%~8.79%; T4 and T6 increased the grain yield of oil flax by 54.7% and 43.5%, respectively; T1, T2, T4 and T6 increased the harvest index of oil flax by 17.4%~43.5%; T4 and T6 were with optimal water use efficiency of oil flax, increasing by 35.6% and 30.7%, respectively.Therefore, T4 is the optimal fertilization option in this experiment.