[Objective] This experiment studied the effects of biochar addition on the content and horizontal transport of NO₃^--N in upland red soil in laboratory to provide scientific bases for water management and environmental protection in the fields.[Methods] Moisture diffusion rate meter was used to determine the horizontal transport velocity and concentration of NO₃^--N in soil at biochar addition rates of 0, 5, 10, 20, 30 and 40 t/hm².[Results] The horizontal transport velocity and concentration of NO₃^--N were significantly affected by biochar addition. A same trend, which performed an increase at first and then a decrease with the biochar application rate increased, was found in the horizontal transport velocity and concentration of NO₃^--N in soil and the diffusivity decreased with the increasing rate of biochar addition. When the application rate of biochar was 30 t/hm², the horizontal transport velocity and concentration of NO₃^--N in soil got the highest, which were 0.67 cm/min and 165.52 mg/kg, respectively. When the application rate of biochar was 40 t/hm², the horizontal transport velocity and concentration of NO₃^--N were lower than those of 30 t/hm². The transport concentration of NO₃^--N reached the maximum value at the surface of wet spearhead in all treatments, which existing on the interface between wet and dry soil. Biochar addition decreased the soil bulk density but increased the soil organic carbon content and total porosity so as to the horizontal transport of NO₃^--N in different treatments were changeable.[Conclusion] Biochar addition can improve the soil properties, and promote the horizontal transport of NO₃^--N in upland red soil. It is very important to pay attention to prevent the pollution of leaching loss of nitrogen and reduce the potential risk of surface water.