The objectives of the research were to investigate the effects of the dicyandiamide(DCD)and 3,4dimethylpyrazole phosphate(DMPP)on transformation of urea nitrogen in chernozem in northeast China.The experiment was conducted under constant temperature,using normal urea as the control check.It was found that DMPP most effectively inhibited the transformation from ammonium nitrogen to nitrate nitrogen,apparent nitrification rate in soil was the lowest and nitrification inhibitory rate in soil was the highest than that in other treatments.DMPP had the longest effective time which was 63 day,while the best effect was up to 42 days,which was much better than that of DCD.Application of DCD also had distinct inhibiting effect on transformation of urea nitrogen,the apparent nitrification rate in soil was lower and nitrification inhibitory rate in soil was higher,and the significant effect time was 35 days,while it could be up to 56 days.The effective time of slow release urea fertilizer was 35 days which could be found evident effect in 7 days.The inhibit effect ranked as DMPP+urea>DCD+urea>slow release urea>urea.