To clarify the changes of soil biological properties of millet field under controlled-release nitrogen fertilizer application in the dryland area of the Loess Plateau of Inner Mongolia，a field experiment was set up to investigate the effects of different reduction treatments of controlled-release nitrogen fertilizer on millets yield and soil enzyme activity and microbial carbon content in different soil layers(0-20 and 20-40 cm)at seedling，tassel and maturity stages，using common urea as control. The results showed that the soil enzyme activity，enzyme composite index and microbial carbon content showed a trend of increasing and then decreasing during the growth period of millets，with the peak occurring at the tassel stage，and the soil biological characteristics between soil layers showed as 0-20 cm better than 20-40 cm，and the effects of different nitrogen fertilizer treatments on the soil biological characteristics of 0-20 cm were higher than those of 0-40 cm. The application of nitrogen fertilizer significantly increased the soil peroxidase，urease，sucrase activity，combined enzyme index and microbial mass carbon content during the millets’ reproductive period by 2.37%-24.37%，3.79%-25.83%，3.65%-33.24%，2.18%-22.51% and 4.09%-26.66%，respectively. The equal application of controlled-release nitrogen fertilizer and the reduction of 20% or less did not significantly affect the soil enzyme activity and microbial mass carbon content of millets at the late stage of fertility compared with normal urea. However，controlled-release nitrogen fertilizer at 30% reduction significantly reduced soil urease activity by 3.65%-7.12% and enzyme composite index by 2.62%-9.60% compared to urea treatment，and controlled-release nitrogen fertilizer at 40% reduction significantly reduced soil catalase activity by 3.65%-7.12%，sucrase activity by 4.85%-16.63% and microbial carbon content by 5.45%-13.90%. The application of equal amount of controlled-release nitrogen fertilizer significantly increased millets yield by 4.42% and significantly reduced millets yield by 3.19%-5.23% at 30%-40% reduction of controlled-release nitrogen fertilizer. In conclusion，the application of controlled-release nitrogen fertilizer did not significantly affect the soil biological properties while improving millets yield，but the soil biological properties deteriorated and millets yield decreased significantly when the controlled-release nitrogen fertilizer was reduced by 30% or more. Therefore，full application of controlled-release nitrogen fertilizer or less than 20% nitrogen reduction should be appropriate for millets production in this region.