Abstract: In this study, to investigate the synergistic effect and appropriate input threshold of urea ammonium nitrate solution (UAN) under drip irrigation of maize, a two-year field experiment was conducted in Qian’an County in the semi-arid region of Jilin Province in 2020 and 2021 using UAN as the test material. The UAN fertilizer application treatments included 0, 100, 140, 180, 220, and 260 kg(N)∙hm⁻², and optimized urea application Urea, 220 kg(N)∙hm⁻² of urea was used as a control. Differences in maize yield, maize components, dry matter accumulation, leaf area index, N use efficiency, soil N content, and apparent soil N balance were studied. The results showed that maize yield was significantly affected by N fertilizer application rates, increasing with the increase in N fertilizer application rates and reaching a yield plateau under 180 kg∙hm⁻² of N fertilizer application rate. The maize yield under N180 treatment 180 kg(N)·hm⁻² of UAN was 2.02% higher than that under the Urea treatment over an average of two years. The yield advantage of the UAN treatments was mainly attributed to the increasing kernel number per ear and 100-kernel weight. The leaf area index, dry matter accumulation amount, translocation amount of dry matter, and contribution rate of dry matter accumulation to grains after the silking stage increased with increasing N fertilizer application rate during the maize growth stages. These values under the UAN treatments with >180 kg(N)∙hm⁻² were no longer significant increased, while all (excluding contribution rate of dry matter accumulation to grains in 2021) were higher than those of Urea treatment. Under UAN treatments, the N recovery efficiency, agronomic N efficiency, and partial factor productivity decreased with increasing N fertilizer application rates. N220 treatment values were increased by 4.45%, 2.09 kg∙kg⁻¹ and 2.09 kg∙kg⁻¹, compared to those of Urea treatment. Compared with the urea treatment, the UAN treatment, under the same N fertilizer application rate, decreased the inorganic nitrogen content in the 60–100 cm soil layer, resulting in a 7.51% reduction in apparent N loss. The UAN application rate of 188.90 kg∙hm⁻² is appropriate when considering maize yield, N recovery efficiency, and soil N apparent loss. The corresponding maize yield, N recovery efficiency, and soil N apparent loss were 11 863.42 kg∙hm⁻², 44.21%, and 151.79 kg(N)∙hm⁻², respectively. Compared with those in the urea treatment, the maize yield and N recovery efficiency under the UAN application rate of 188.90 kg∙hm⁻² increased by 4.78% and 7.61%, respectively, and the N fertilizer application rate and N apparent loss decreased by 14.14% and 29.55%, respectively. The N fertilizer application rate was calculated as 179–198 kg(N)∙hm⁻² using 95% as the highest theoretical yield in the confidence interval. In conclusion, compared with the urea application, the application of UAN reduced the total N input and apparent N loss, and achieved higher maize yield and N use efficiency. This is an effective method to achieve nitrogen reduction and efficiency enhancement in maize in the semi-arid region of Northeast China.