Adding different exogenous nitrogen (N) sources is essential for soil N transformation. In this study, soil under long-term cultivation was selected to conduct the indoor incubation experiment, in which five treatments were designed in order to analyze the effects of adding different exogenous N sources on soil ammonium N (NH₄⁺), nitrate N (NO₃^–), dissolved organic N (DON), and microbial biomass N (MBN), the designed treatments were as follows: 1) control(CK), 2) adding Urea at N 150 kg/hm² (U₁₅₀), 3) adding rice straw (equal to adding N 38 kg/hm², Straw), 4) adding urea and straw (equal to adding N 188 kg/hm², U₁₅₀+Straw), and 5) adding urea at N 188 kg/hm² (U₁₈₈). The results showed that soil NH₄⁺ increased first and then decreased during the incubation period, soil NH₄⁺ of treatments adding with urea reached the peak value more rapidly than those adding with straw. Soil NO₃^– content increased with time. Total mineral N of U₁₈₈ treatment was higher than that of U₁₅₀+Straw treatment during the period of incubation. Compared with U₁₅₀ treatment, soil mineral N content was lower in U₁₅₀+Straw treatment but became a little higher after 30 days of incubation. Compared with CK, adding different exogenous N source increased soil mineral N by 169.61% ~ 496.75% at the end of incubation. MBN and DON of treatments with adding different exogenous N sources reached maximum values at 10 days or 30 days after incubation and then decreased with time. MBN and DON of treatments with adding straw and/or straw+urea were higher than those with adding urea only during the prior stage of incubation. The results demonstrated that adding exogenous N sources of organic material mainly increased soil organic N.