A long-term rainfed field experiment comparing the effects of different succeeding crops of lucerne on soil organicnitrogen composition was conducted on the Loess Plateau in2012.Six succeeding crops of lucerne[lucerne continuouscropping(LC)，lucerne -fallow(LF)，lucerne -fallow-wheat(L FW)，lucerne -fallow-corn(LFC)，lucerne -potato(LP) and lucerne-millet(LMi)]werecompared.The results showed that the soil total nitrogen content of different succeedingcrops of lucerne gradually decreased with the deepening of the soillayer，In the 0～ 10 cm soillayer，LC had the highesttotal nitrogen content among treatments.Compared with LC，the total nitrogen contents of LMi，LP，L FW，L FC and LFwere decreased by21.62%，14.27%，18.98%，13.41% and 6.15%respectively.The soil microbial biomass nitrogen wasconsistent with the trend of soil total nitrogencontent.Among all the soil organic nitrogen forms under different succeedingcrops of lucerne，acid hydrolysable nitrogen was dominant in soil total nitrogen.The content of hydrolysable unidentifiedN in acid hydrolysable organic nitrogen was the highest，followed by amino acid nitrogen and amino sugar nitrogen.The difference of acid hydrolysable nitrogen components in 0～10 cm soil layer was significant.Compared with the lucernecontinuous cropping，the total nitrogen content of the remaining acidification was reduced，the decline was 11.90% to35.98%.The content of amino acid nitrogen decreased by 10.29% to37.83%，the content of acid -decomposed ammonianitrogen decreased by 24.11% to39.73%，and the content of hydrolysable unidentified N in acid treatment of LF and LPincreased by 10.76% and 3.39% respectively.The hydrolysable unidentified N content of LMi，L FC and LFW treatmentsdecreased by9.34%，43.62% and65.18%，respectively.Amino acid nitrogen was positively correlated with soil totalnitrogen and microbial biomass nitrogen.Therefore，the implementation of the continuous cropping system in the rain -fedagriculture area of the Loess Plateau can maintain the effective composition of soil organicnitrogen，which is conducive to thesustainable development of agriculture in theregion.