The objective of this study was to determine the effects of combined biochemical inhibitors on the transformation and leaching loss of NO₃^--N and NH₄⁺-N from urea-based fertilizer in yellow clayey soil. A soil column leaching experiment was conducted in a greenhouse to observe nitrogen (N) transformation and leaching loss following the application of urea and UAN (300 kg N/hm²) with a urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT), a nitrification inhibitor 2-chloro-6-(trichloromethyl) pyridine (CP), or both. The results showed that the contents of NH₄⁺-N and NO₃^--N from the leacheate of urea and UAN both rose first and then fell with different peak times. The differences in the leaching loss of NH₄⁺-N and NO₃^--N across treatments increased over time. NBPT can slow urea hydrolysis, and effectively inhibit the generation of NH₄⁺-N to retard the peak time and reduce NH₄⁺-N loss. CP can effectively inhibit the transformation of NH₄⁺-N to NO₃^--N to reduce NO₃^--N loss. Compared with the application of NBPT and CP alone, their combination exhibited a synergistic inhibition effect on N leaching loss in yellow clayey soil, namely not only did it slow down urea hydrolysis and maintain high NH₄⁺-N content in the soil, but it also reduced NO₃^--N content in the leacheate. At the end of the incubaton (72 days), the leaching loss of NO₃^--N, NH₄⁺-N, and mineral N, and nitrification rate from UAN treatment were higher than those from the U treatment by 34.39%, 5.32%, 31.72%, and 15.71%, repectively. Compared with the U treatment, U+NBPT, U+CP, and U+NBPT+CP treatments significantly reduced the leaching loss of NO₃^--N by 15.58%, 114.77%, and 73.45%, respectively. Compared with UAN treatment, UAN+NBPT, UAN+CP, and UAN+NBPT+CP treatments significantly reduced leaching loss by 15.88%, 54.87%, and 37.46%, respectively. The leaching loss of NO₃^--N from different treatments ranked UAN > UAN+NBPT > U > UAN+NBPT+CP > U+NBPT > UAN+CP > U+NBPT+CP > U+CP > CK. Within a certain range of fertilizer rate, adding NBPT and CP alone or both can reduce NO₃^--N leaching loss in yellow clayey soil. Equation models were used to describe the relationship between NO₃^--N leaching loss (y) and time (x). The linear equation (y=ax+b) fit well, a and b values in adding inhibitor treatments were obviously different. In conclusion, application of NBPT in yellow clayey soil combined with CP can significantly reduce the leaching loss of soil NO₃^--N and N leaching risk, to improve fertilizer use efficiency.