Abstract: Abstract: Agricultural intensification has led to high inputs of nitrogen fertilizers into cultivated land. Addition of urease and nitrification inhibitor to fertilizers can increase N uptake and reduce N losses, but field studies have shown that their efficiency varies greatly on the environmental conditions. Soil temperature and water content are key factors controlling urea hydrolysis in soils and are also key parameters for the variation in inhibition effect of urease and nitrification inhibitors. The objective of this study was to compare the inhibition effects of biochemical inhibitor combinations on soil nitrogen transformation, and to determine the effects of different soil temperature and water content on the inhibition of urea hydrolysis. We investigated the inhibition effect of combined biochemical inhibitors (N-(n-butyl) thiophosphoric triamide, NBPT / N-(n-propyl) thiophosphoric triamide, NPPT + 2-chloro-6(trichloromethyl) pyridine, CP) on urea-nitrogen transformation as affected by soil water content (60% and 80% water holding capacity, WHC) and soil temperature (15, 25 and 35 ℃) interaction in yellow clayey soil using an 30-day aerobic incubation test. Results showed that soil temperature and water content had significant effects on the inhibition effects of inhibitor combinations in yellow clayey soil (P < 0.05), especially soil temperature. With the increase of soil temperature, urea hydrolysis increased by the effective time of the combinations reduced, and the inhibition effect of urease and nitrification weakened accompanied by increase in nitrification. With the decrease of soil water content, urea hydrolysis tended to slow by the effective time of the combinations prolonged, and the inhibition effect of urease and nitrification increased accompanied by nitrification weakened. The urease inhibition rate (Day 1) and nitrification inhibition rate (Day 30) under different soil water content treatments ranked as 60%WHC> 80%WHC, and apparent nitrification rate (Day 30) ranked as 60%WHC< 80%WHC. The urease inhibition rate (Day 3) and nitrification inhibition rate (Day 30) under different soil temperature treatments ranked as 25 ℃>15 ℃>35 ℃, and apparent nitrification rate (Day 30) ranked as 25℃> 35 ℃>15 ℃. The urease inhibition rate (Day 3) under different biochemical inhibitor combinations ranked as U+NBPT> U+NPPT>U+NPPT+CP>U+NBPT+CP>U+CP, and nitrification inhibition rate (Day 30) ranked as U+CP>U+NBPT+CP> U+NPPT+CP>U+NPPT>U+NBPT, and apparent nitrification rate (Day 30) ranked as CK>U>U+NPPT>U+NBPT> U+NPPT+CP>U+NBPT+CP>U+CP. NBPT/NPPT or combined with CP treatments can effectively inhibit soil urease activity, and slow urea hydrolysis. CP or combined with NBPT/NPPT treatments can effectively inhibit the transformation of NH4+-N to NO3--N, and keep high NH4+-N content in soil for longer time under different soil temperature and water content conditions. Application of a new urease inhibitor NPPT alone or with CP had the similar inhibition effect of soil urea hydrolysis with that of NBPT. The optimum condition of soil temperature and water content by the application of biochemical inhibitor combinations in yellow clayey soil were 25℃ and 60%WHC, respectively. In conclusion, urea application combined with both urease inhibitor and nitrification inhibitor should be adopted in yellow clayey soil according to different soil temperature and water content conditions.