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Atmospheric nitrogen (N) and acid deposition have become global environmental issues and are likely to alter soil respiration (Rs); the largest CO2 source is from soil to the atmosphere. However, to date, much less attention has been focused on the interactive effects and underlying mechanisms of N and acid deposition on Rs, especially for ecosystems that are simultaneously subjected to elevated levels of deposition of both N and acid. Here, to examine the effects of N addition, acid addition, and their interactions with Rs, we conducted a two-way factorial N addition (control, CK; 60 kg N ha−1 a−1, LN; 120 kg N ha−1 a−1, HN) and acid addition (control, CK; pH 4.5, LA; pH 2.5, HA) field experiment in a subtropical plantation in China. Our results showed the following: (1) During the one-year observation period, the seasonal dynamics of Rs presented a single peak curve model, which was closely related to the surface soil temperature. (2) The simulated N deposition and acid deposition significantly decreased the Rs in the subtropical plantation. Compared to the CK plots, the LN and HN treatments reduced the annual mean values of Rs by 41% and 56%, and the annual mean values of Rs were inhibited by 26% and 31% in the LA and HA plots. The inhibition of N application on Rs was stronger than that of the simulated acid deposition. (3) Significant interactions between N addition and acid addition on Rs were detected, and Rs was significantly inhibited under four co-addition treatments. (4) The underlying mechanism and main reason for the responses of Rs to simulated N and acid deposition in this study might be the inhibition of soil microbial biomass and soil enzyme activity due to soil acidification under increased N and acid input.