In order to understand how cold-water irrigation at booting stage affects the dry matter and nitrogen accumulation of grain in rice in cold-region, two japonica rice (Dongnong 428 and Songjing 10) were subjected to cold water irrigation for 6 varying length of time (0, 3, 6, 9,12 and 15 d) at booting stage. The dry matter, nitrogen accumulation and enzyme activities involved in nitrogen metabolism of grain were measured,respectively. The results showed that grain dry matter accumulation and yield in rice in cold-region followed a similar trend, and decreased under cold-water irrigation at booting stage with increasing cold-water irrigation days compared with the control. Due to the decreased maximum accumulation rate, seed setting rate, productive panicle number, grain number per panicle, grain dry matter accumulation decreased. The total nitrogen, protein nitrogen of grain, protein content of mature grain, and glutamine synthetase activity at early grain filling stage increased under cold-water irrigation. The gutamic-pyruvic transaminase and glutamic-oxaloacetic transaminase activities in grain significantly increased under 6 d of cold-water irrigation, whereas significantly decreased under 9-15 d of cold-water irrigation. The increase in total and protein nitrogen contents was due to the enhancement of grain nitrogen assimilation and protein synthesis ability under short term (3-6 d) cold-water irrigation, however, the process of nitrogen assimilation was inhibited, affecting the synthesis of protein and amino acid, eventually leading to a reduction in the growth rate of grain nitrogen content under long term(9-15 d) cold-water irrigation. Given grain total nitrogen, protein nitrogen and granule starch protein content varied with cold-water treatment duration and cultivar, they can be used as comprehensive evaluation indicators for cold resistance.