Under hydroponic condition，this paper studies the effect of different ammonium and nitrate ratio（CK，0∶100；T1，10∶90；T2，25∶75；T3，50∶50）on lettuce（Lactuca sativa L.）growth and N，P，K accumulation．The results showed that compared with the CK，T1 significantly promoted the lettuce growth，and its fresh weight of aerial part and economic yield were increased by 15.77% and 15.21%，while the fresh weight of aerial part and economic yield in T2 and T3 treatments were significantly reduced．The N，P，K accumulation in lettuce plant were behaved as T1 ＞ CK ＞ T2 ＞ T3 under different ammonium and nitrate ratio treatment．There were significant differences existing among treatments．The nitrogen loss ratios of each treatment
under hydronic cultivation were between 20.17%-65.31%.Compared with the CK，the nitrogen loss amount and loss rate under T1 treatment were reduced by 14.79% and 4.24 percentage points，respectively，while the nitrogen loss amount and loss rate under T2 and T3 treatments were significantly increased．The plant growth and N，P，K accumulation were improved by 10% ammonium in nutrient solution，and yet its nitrogen loss was reduced significantly．