Abstract: Objectives Artificial surface application in paddy fields after the transplanting is one of the main reasons resulting in low nitrogen use efficiency. This paper mainly discussed effect of mechanized topdressing polymer-coated mixed fertilizer on rice yield and nitrogen use efficiency.Methods The experiments were conducted at Daxing Farm in Heilongjiang Province from 2013 to 2015. Under the same total fertilizer and base fertilizer dosages, the control topdressing was urea broadcasting at tillering stage and heading stage of rice; the treatment topdressing was mechanized topdressing of two kinds of polymer-coated urea, the theoretical release duration was 50 days (OPT1) and 60 days (OPT2), which were mixed with compound fertilizers and applied at 5 cm deep beside the seedling roots. Laboratory and field experiments were conducted to measure the release rate of the polymer-coated urea, nitrogen accumulation and rice yield were analyzed.Results The release durations of the two kinds of polymer-coated urea (release rate were 80%) were approximately 40 days and 70 days in 25℃ water, respectively, and those in the field were 50 days and 80 days, respectively. Compared with the rice treated with conventional fertilizer practice, the rice treated with mechanical side dressing had shorter time for the reviving of seedlings, and the tiller number at the earlier stage and the highest tiller number were higher, and the rice harvest panicles were significantly increased by 15.8%-21.1% (P 0.05), in spite of that rice tiller spike rate was increased slightly. The OPT1 and OPT2 increased rice yields by 13.35% and 18.69% (P 0.05). The mechanized topdressing method increased nitrogen accumulation and dry matter accumulation of rice plants significantly during the whole growth stage. The comprehensive average income was about 3000 yuan/hm2 due to the significant increase of rice yield in OPT1 and OPT2, although a little bit of increase in fertilizer cost.Conclusions The mechanized topdressing polymer-coated mixed fertilizer could achieve the goal of deep fertilization in paddy field, increase the rice yield and nitrogen use efficiency.