[Objective]To investigate the effects of different litter inputs on soil nitrogen components during the process of returning farmland to forest in the typical black soil region and to provide a theoretical basis for soil nutrient regulation, tree species selection, and vegetation restoration, this study conducted a short-term indoor simulation experiment. [Methods]The experiment included three treatments—Populus alba litter, Larix gmelinii litter, and maize straw—along with a blank control. Each type of litter was mixed with air-dried soil and incubated at 25 °C for 28 days. Soil total nitrogen (TN), available nitrogen (AN), microbial biomass nitrogen (MBN), inorganic nitrogen (NH4+-N, NO3–-N), urease (URE), and β-glucosidase (BG) were measured. Variance analysis and Pearson correlation were employed to investigate the differences in soil nitrogen content and enzyme activities under the input of different types of litterfall in typical black soil. [Results]Variance analysis showed that at 3, 7, 14, and 28 days, the TN values in the Populus alba litter treatment were significantly higher than those in the control, Larix gmelinii litter, and maize straw treatments (P < 0.05). The input of the three types of litter did not significantly affect soil AN content. For MBN, the Populus alba litter treatment showed a significantly greater increase at 7 and 14 days compared with the control and the other two treatments (P < 0.05). At 28 days, MBN values in both the Populus alba and Larix gmelinii litter treatments were significantly higher than those in the control and maize straw treatments (P < 0.05). All litter treatments significantly reduced soil inorganic nitrogen content. BG was highly or significantly negatively correlated with NH4+-N and NO3–-N, while it was highly positively correlated with URE, TN, and AN. URE was significantly or highly significantly correlated with TOC, MBN, and TN and negatively correlated with NH4+-N. [Conclusion]The comprehensive experimental results indicate that the decomposition of the three types of exogenous inputs is closely related to the contents of total nitrogen, available nitrogen, microbial biomass nitrogen, inorganic nitrogen, and enzyme activity in the soil. The input of litterfall facilitates soil nutrient cycling and accumulation, with the litterfall of *Populus alba × glandulosa* (a broad-leaved tree species) demonstrating the most significant effect on improving soil nitrogen content and enzyme activity.